#1MAINST CAPITAL CORPORATION Debt Capital Markets Presentation First Quarter - 2023 Main Street Capital Corporation NYSE: MAIN mainstcapital.com#2Disclaimers Main Street Capital Corporation (MAIN) cautions that statements in this presentation that are forward-looking, and provide other than historical information, involve risks and uncertainties that may impact our future results of operations. The forward-looking statements in this presentation are based on current conditions as of May 5, 2023, and include, but are not limited to, statements regarding our goals, beliefs, strategies, future operating results and cash flows, operating expenses, investment originations and performance, available capital, payment and the tax attributes of future dividends and shareholder returns. Although our management believes that the expectations reflected in any forward-looking statements are reasonable, we can give no assurance that those expectations will prove to have been correct. Those statements are made based on various underlying assumptions and are subject to numerous uncertainties and risks, including, without limitation: our continued effectiveness in raising, investing and managing capital; adverse changes in the economy generally or in the industries in which our portfolio companies operate; the impacts of macroeconomic factors on MAIN and its portfolio companies' business and operations, liquidity and access to capital, and on the U.S. and global economies, including impacts related to the COVID-19 pandemic and other public health crises, risk of recession, inflation, supply chain constraints or disruptions and rising interest rates; changes in laws and regulations or business, political and/or regulatory conditions that may adversely impact our operations or the operations of our portfolio companies; the operating and financial performance of our portfolio companies and their access to capital; retention of key investment personnel; competitive factors; and such other factors described under the captions "Cautionary Statement Concerning Forward-Looking Statements," "Management's Discussion and Analysis of Financial Condition and Results of Operations" and "Risk Factors" included in our filings with the Securities and Exchange Commission (www.sec.gov), including our most recent annual report on Form 10-K and subsequently filed quarterly reports on Form 10-Q. We undertake no obligation to update the information contained herein to reflect subsequently occurring events or circumstances, except as required by applicable securities laws and regulations. Main Street Capital Corporation MAIN ST CAPITAL CORPORATION MAIN has filed a registration statement (which includes a prospectus) with the SEC for any offering to which this communication may relate and may file one or more supplements to the prospectus in the future. Before you invest in any of MAIN's securities, you should read the registration statement, the prospectus and the applicable prospectus supplement(s) in order to fully understand all of the implications and risks of an offering of MAIN's securities. You should also read other documents MAIN has filed with the SEC for more complete information about MAIN and its securities offerings. You may access these documents for free by visiting EDGAR on the SEC website at www.sec.gov. Alternatively, MAIN will arrange to send you any applicable prospectus and prospectus supplement if you request such materials by calling us at (713) 350-6000. These materials are also made available, free of charge, on our website at www.mainstcapital.com. Information contained on our website is not incorporated by reference into this communication. The summary descriptions and other information included herein are intended only for informational purposes and convenient reference. The information contained herein is not intended to provide, and should not be relied upon for, accounting, legal or tax advice or investment recommendations. Before making an investment decision with respect to MAIN, investors are advised consult with their tax, financial, investment and legal advisors. NYSE: MAIN mainstcapital.com Page 2#3Main Street Capital Corporation 1st Quarter - 2023 Main Street Capital Corporation MAIN ST CAPITAL CORPORATION NYSE: MAIN mainstcapital.com Page 3#4MAIN is a Principal Focus on unique Lower Middle Market debt and equity investment strategy, Asset Management Business and internally managed operating structure differentiates MAIN from other investment firms Conservative capital structure with multiple issuer investment grade ratings ● S&P BBB-/stable outlook Fitch BBB-/stable outlook Investor in Private Debt and Equity Internally-managed Business Development Company (BDC) IPO in 2007 Approximately $6.6 billion in capital under management (¹) Approximately $5.0 billion internally at MAIN(¹) Over $1.6 billion as the investment adviser to external parties (¹) ● Primarily invests in the under-served Lower Middle Market (LMM) ● ● ● Proprietary debt investments in privately held companies typically owned by private equity sponsors (Private Loans) Originated directly by MAIN or through strategic relationships with other investment funds First lien, senior secured debt investments Companies consistent with size of the companies in MAIN's LMM and Middle Market investment strategies ● MAIN ST CAPITAL CORPORATION . Targets companies with revenue between $10 million - $150 million; EBITDA between $3 million $20 million ● Provides single source solutions, including a combination of first lien, senior secured debt and equity financing Debt investments in Middle Market companies First lien, senior secured and/or rated debt investments Larger companies than LMM investment strategy Attractive asset management advisory business Significant management ownership / investment in MAIN Headquartered in Houston, Texas (1) Capital under management includes undrawn portion of debt capital as of March 31, 2023 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 4#5Investment Portfolio - By Type of Investment (¹) Other Portfolio (2) Equity, 2.8%, $116.1m Total Investment Portfolio $4.2 billion Equity, 26.5%, $1.1b Debt Investments, 70.7%, $2.9b (1) Fair value as of March 31, 2023 (2) Other portfolio investments, as described in MAIN's SEC filings Main Street Capital Corporation NYSE: MAIN Total Debt Investments $2.9 billion First Lien Debt, 99.2%, $2.9b MAIN ST CAPITAL CORPORATION Junior Debt, 0.8%, $24.8m mainstcapital.com Page 5#6Unique Investment Strategy MAIN's investment strategy differentiates MAIN from its competitors and provides highly attractive risk-adjusted returns Main Street Capital Corporation ● ● ● Lower Middle Market (LMM) Proprietary investments that are difficult for investors to access Companies with $10 million - $150 million of revenues and $3-$20 million of EBITDA Customized financing solutions which include a combination of first lien, senior secured debt and equity Large addressable market High cash yield from debt investments Dividend income, NAV growth and net realized gains from equity investments Middle Market Larger companies than LMM strategy, with EBITDA between $20 - $100 million First lien, senior secured debt investments Floating rate debt investments Large addressable market Can provide source of liquidity for MAIN as needed NYSE: MAIN MAIN ST CAPITAL CORPORATION ● Private Loans Companies that are similar in size to companies in LMM and Middle Market First lien, senior secured debt investments in privately held companies originated directly by MAIN or through strategic relationships with other investment funds Floating rate debt investments Proprietary investments that can be difficult for investors to access Investments with attractive risk-adjusted returns Asset Management Business Monetizing value of MAIN's intangible assets Significant contribution to net investment income Source of stable, recurring fee income Returns benefit MAIN stakeholders due to internally managed structure mainstcapital.com Page 6#7Portfolio Highlights (1) The benefits of MAIN's unique investment strategy have resulted in a high quality, diversified and mature investment portfolio ● ● ● ● Lower Middle Market $2.1 billion of total investments 79 companies $1.2 billion of debt investments (58%) $896.3 million of equity investments (42%) Typical initial investment target of 75% debt / 25% equity 99% of debt investments are first lien (²) Average investment size of $26.7 million at fair value or $21.9 million at cost Weighted-average effective yield on debt of 12.6% (3) Middle Market $306.2 million of total investments 30 companies $297.3 million of debt investments (97% of Middle Market portfolio) 99% of debt investments are first lien(2) Average investment size of $13.0 million (²) 95% of debt investments bear interest at floating rates (2) Weighted-average effective yield of 11.8% (³) (1) As of March 31, 2023; investment amounts at fair value, unless otherwise noted (2) As of March 31, 2023; based on cost . ● ● ● ● ● ● MAIN ST CAPITAL CORPORATION Private Loans $1.5 billion of total investments 86 companies $1.4 billion of debt investments (96% of Private Loan portfolio) 99% of debt investments are first lien(²) Average investment size of $17.8 million (2) 98% of debt investments bear interest at floating rates (2) Weighted-average effective yield of 12.4% (³) Total Portfolio(4) $4.2 billion of total investments 211 companies $2.9 billion of debt investments (71%) $1.2 billion of equity investments (29%), including $116.1 million of Other Portfolio investments 99% of debt investments are first lien(²) 73% of debt investments bear interest at floating rates (2) Weighted-average effective yield on debt investments of 12.5% (³) (3) As of March 31, 2023; weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status (4) Includes $132.7 million of fair value ($29.5 million of cost basis) of equity investment relating to MAIN's wholly-owned unconsolidated subsidiary, MSC Adviser I, LLC (the External Investment Manager), and $1.9 million of fair value ($2.0 million of cost basis) of a short-term portfolio investment Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 7#8Business Development Company (BDC) Background Created by Congress in 1980 through the Small Business Investment Incentive Act of 1980 to facilitate the flow of capital to small and mid- sized U.S. businesses Highly regulated by the Securities and Exchange Commission under the Investment Company Act of 1940 (1940 Act) Provide a way for individual investors to participate in debt and equity investments in private companies Main Street Capital Corporation Leverage Regulatory restrictions on debt leverage levels require BDCs to maintain conservative leverage Must maintain an asset to debt coverage ratio of at least 1.5x ● Full Transparency Detailed schedule of all investments (and related key terms) in quarterly and annual reporting Quarterly fair value mark to market accounting ● ● Income Tax Treatment As a Regulated Investment Company (RIC), BDCs generally do not pay corporate income taxes ● MAIN ST CAPITAL CORPORATION ● ● To maintain RIC status and avoid paying corporate income taxes, BDCs must distribute at least 90% of taxable income (other than net capital gain) to investors To avoid a 4% federal excise tax on undistributed income, BDCs must distribute in each calendar year the sum of (1) 98% of their net ordinary income for the calendar year and (2) 98.2% of their realized capital gains (both long-term and short-term) Tax treatment is similar to Real Estate Investment Trusts (REITS) NYSE: MAIN mainstcapital.com Page 8#9MAIN Capital Structure E Current capitalization ($ in 000's) Cash Credit Facilities (1) July 2026 Notes(2) May 2024 Notes (2) December 2025 Notes (2) Total non-SBIC debt SBIC Debentures(²) Total debt Book value of equity Total capitalization Debt / Capitalization Debt / Book equity Debt / Enterprise value (³) Debt / Market capitalization (3) Stock price / Net asset value per share(³) (2) Debt amounts reflected at par value Based on stock price of $39.46 as of March 31, 2023 $ Main Street Capital Corporation $ SA 3/31/2023 39,752 564,000 500,000 450,000 150,000 1,664,000 334,000 1,998,000 2,172,922 4,170,922 NYSE: MAIN 0.48x 0.92x 0.40x 0.64x 1.45x MAIN ST CAPITAL CORPORATION % of Capitalization 13.5 % 12.0% (1) Includes MAIN's corporate revolving credit facility (the Corporate Facility) and SPV credit facility (the SPV Facility and together, the Credit Facilities); see page 18 for further detail related to MAIN's Credit Facilities 10.8 % 3.6 % 39.9 % 8.0 % 47.9 % 52.1 % 100.0 % mainstcapital.com Page 9#10Conservative Leverage EN As of March 31, 2023 ($ in 000's) Total Assets Debt Capital: Credit Facilities (1) SBIC Debentures Notes Payable (²) Total Debt Net Asset Value (NAV) Key Leverage Stats Interest Coverage Ratio (³) Asset Coverage Ratio (4) Consolidated Asset Coverage Ratio - Regulatory(5) Debt to Assets Ratio Debt to NAV Ratio (6 (6) Net Debt to NAV Ratio (7)(8) $ $ Non-SBIC 3,624,263 $ 564,000 1,097,435 1,661,435 $ 1,839,711 $ SBICS 668,992 $ 328,206 328,206 $ 333,211 $ 6.19x 2.00x N/A 0.49x 1.00x MAIN ST CAPITAL CORPORATION 0.98x Total 4.05x 2.18x N/A 0.46x 0.90x 0.89x (1) Includes MAIN's corporate revolving credit facility (the Corporate Facility) and SPV credit facility (the SPV Facility and together, the Credit Facilities); see page 18 for further detail related to MAIN's Credit Facilities 4,293,255 564,000 328,206 1,097,435 1,989,641 2,172,922 4.33x 2.15x 2.30x 0.46x 0.92x 0.90x (2) Includes the carry value of the July 2026 Notes ($498.3 million; $500.0 million par), the May 2024 Notes ($450.6 million; $450.0 million par) and the December 2025 Notes ($148.6 million; $150.0 million par) (3) Distributable Net Investment Income (DNII)(8) + interest expense / interest expense on a trailing twelve-month basis (4) Calculated as total assets divided by total debt at par, including SBIC Debentures ($334.0 million), July 2026 Notes ($500.0 million), May 2024 Notes ($450.0 million) and December 2025 Notes ($150.0 million) (5) Calculated per BDC regulations; SBIC Debentures are not included as "senior debt" for purposes of the BDC asset coverage requirements pursuant to exemptive relief received by MAIN (6) Debt to NAV Ratio is calculated based upon the par value of debt (7) Net debt in this ratio includes par value of debt less cash and cash equivalents of $33.3 million, $6.5 million and $39.8 million for the Non-SBIC, SBICs and Total, respectively (8) See Non-GAAP Information disclosures on page 37 and reconciliation of DNII to Net Investment Income on page 39 of this presentation Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 10#11Conservative Leverage - Regulatory Passage of the Small Business Credit Availability Act in December 2017 provided the opportunity for BDCs to obtain board or shareholder approval to access additional leverage by lowering the required asset coverage to 1.50x MAIN received shareholder approval, effective as of May 3, 2022, to adopt the 1.50x asset coverage ratio MAIN has historically operated at conservative regulatory leverage levels, in all cases with significant cushion to the 1.50x regulatory limits, and proven through historical performance that MAIN does not require access to additional leverage to generate market leading returns MAIN's Historical Asset Coverage Ratio: Consolidated Asset Coverage Ratio - Regulatory(¹) Prior Minimum Required Asset Coverage (2) Cushion % above Prior Minimum Required Asset Coverage Current Minimum Required Asset Coverage (²) Cushion % above Current Minimum Required Asset Coverage 2018 3.22x 2.00x 61% 1.50x 115% 2019 2.89x 2.00x 45% 1.50x 93% 2020 2.67x 2.00x 34% 1.50x 78% 2021 2.22x 2.00x 11% 1.50x MAIN ST CAPITAL CORPORATION 48% 2022 2.27x N/A N/A 1.50x 51% Q1 2023 2.30x N/A N/A 1.50x 53% (1) Calculated per BDC regulations; SBIC Debentures are not included as "senior debt" for purposes of the Minimum Asset Coverage Ratio requirements pursuant to exemptive relief received by MAIN (2) We received shareholder approval, effective as of May 3, 2022, to adopt the 1.5x asset coverage ratio (decreased from the previously required asset coverage ratio of 2.0x) Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 11#12Conservative Leverage - Excess Collateral Improves Over Time MAIN's conservative use of leverage and equity to fund its growth results in significant excess collateral that provides protection to lenders MAIN's management of its capital structure results in reduced risk profile for debt investors over time Excess collateral available to unsecured lenders has increased by 218% since MAIN's first investment grade (IG) debt issuance ($ millions) Total Assets Excluding SBIC Assets Add: Equity Value of SBIC Entities (2) Total Collateral Available to Secured Lenders Less: Secured Debt (Credit Facilities) Excess Collateral Available to Unsecured Lenders Increase since first IG debt issuance(3) Less: Unsecured Debt Outstanding (par value) Remaining Excess Collateral Available to Unsecured Lenders Increase since first IG debt issuance(3) 9/30/2014 (1) 3/31/2023 $ 1,137 218 1,355 $ $ $ (287) 1,068 (91) MAIN ST CAPITAL CORPORATION 977 (2) (3) First IG notes issued in November 2014 (4) Includes additional IG debt issuances in April 2019, December 2019, July 2020, January 2021, October 2021, December 2022 and February 2023 Main Street Capital Corporation NYSE: MAIN $ $ $ 3,624 333 3,957 (564) 3,393 218 % (1,100) 2,293 135 % (4) Most recent information publicly reported prior to first IG debt issuance Represents asset value in excess of SBIC debt (par value); SBIC assets contain negative pledge in relation to SBIC debt; therefore, equity at SBIC entities is effectively collateral for lenders mainstcapital.com Page 12#13Key Credit Highlights Experienced Management Team with Strong Track Record Efficient and Leverageable Internally Managed Operating Structure Conservative Leverage Unique Investment Strategy High Quality Portfolio Main Street Capital Corporation ● ● ● ● ● ● ● ● ● ● Management team has over 100 years of collective investment experience and relationships MAIN ST CAPITAL CORPORATION Long-term working relationships together dating back over 20 years Significant management equity ownership Meaningful operating cost advantage through efficient internally managed structure Significant benefits through alignment of interests between management (stock ownership and incentive compensation) and investors Industry leading operating expense efficiency 1940 Act requires MAIN to maintain a minimum 1.5x regulatory asset coverage ratio MAIN's asset coverage ratio is ~2.3x on a regulatory basis excluding SBIC Debentures; ~2.1x on a consolidated basis including SBIC debentures Conservative leverage position further enhanced raises through at-the-market, or ATM, equity issuance program ongoing efficient capital Unique investment strategy differentiates MAIN from its competitors and provides highly attractive risk-adjusted returns Asset management advisory business significantly enhances MAIN's returns to its investors NYSE: MAIN Significant diversification Debt investments primarily carry a first priority lien on the assets of the business Permanent capital structure of BDC allows for long-term, patient investment strategy and overall approach mainstcapital.com Page 13#14MAIN Executive Management Team Dwayne Hyzak (1)(2) CEO David Magdol(¹)(2) President and CIO (³) Jesse Morris (1) CFO, COO, EVP Jason Beauvais; JD(1) EVP, GC, CCO(4) and Secretary ● ● ● ● ● Co-founded MAIN; Joined Main Street group in 2002; affiliated with Main Street group since 1999 Director of Acquisitions & Integration with Quanta Services (NYSE: PWR) Manager with a Big 5 Accounting Firm's audit and transaction services groups Co-founded MAIN; Joined Main Street group in 2002 Vice President in Lazard Freres Investment Banking Division Vice President of McMullen Group (John J. McMullen's Family Office) MAIN ST CAPITAL CORPORATION Joined MAIN in 2019 Executive Vice President with Quanta Services (NYSE: PWR) Vice President and CFO Foodservice Operations with Sysco Corporation (NYSE: SYY) Manager with a Big 5 Accounting Firm Joined MAIN in 2008 Attorney for Occidental Petroleum Corporation (NYSE: OXY) Associate in the corporate and securities section at Baker Botts LLP (1) Member of MAIN Executive Committee (2) Member of MAIN Investment Committee; Vince Foster, MAIN's Chairman of the Board, is also a member of MAIN's Investment Committee (3) Chief Investment Officer (4) Chief Compliance Officer Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 14#15Significant Management Ownership / Investment # of Shares 3,293,812 Significant equity ownership by MAIN's management team, coupled with internally managed structure, provides alignment of interest between MAIN's management and our shareholders Management (1) (2) NYSE: MAIN MAIN ST CAPITAL CORPORATION Market Value (3) $129,973,822 (1) Includes members of MAIN's executive and senior management team and the members of MAIN's Board of Directors (2) Includes 1,238,532 shares, or approximately $34.0 million, purchased by management as part of, or subsequent to, the MAIN IPO, including 19,375 shares, or approximately $0.8 million, purchased, directly or through MAIN's dividend reinvestment plan, in the quarter ended March 31, 2023 (3) Based upon closing market price of $39.46/share on March 31, 2023 Main Street Capital Corporation mainstcapital.com Page 15#16Efficient and Leverageable Operating Structure MAIN's internally managed operating structure provides significant operating leverage and greater returns for our stakeholders "Internally managed" structure means no external management fees or expenses are paid ● Alignment of interest between management and investors Greater incentives to maximize increases to shareholder value and rationalize debt and equity capital raises 100% of MAIN's management efforts and activities are for the benefit of MAIN investors ● MAIN ST MAIN targets total operating expenses (¹) as a percentage of average assets (Operating Expense to Assets Ratio) at or less than 2% ● CAPITAL CORPORATION ● Long-term actual results have significantly outperformed target An industry leading position in cost efficiency, with an Operating Expense to Assets Ratio of 1.4% (²) Significant portion of total operating expenses (¹) are non-cash Non-cash compensation expenses(³) were 24.9% (²) of total operating expenses (1) (1) Total expenses excluding interest expense (2) Based upon the trailing twelve month period ended March 31, 2023 (3) See non-GAAP information disclosures on page 37 and calculation of non-cash compensation expenses on page 39 of this presentation Main Street Capital Corporation NYSE: MAIN Operating Expense to Assets Ratio of 1.1%(²) excluding non-cash compensation expenses (³) mainstcapital.com Page 16#17MAIN Maintains a Significant Operating Cost Advantage Operating Expenses (¹) as a Percentage of Total Assets 3.0% 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% MAIN (2) MAIN Excl. Non-cash Comp Exp (3)(4) Other BDCS (4)(5)(6) MAIN ST CAPITAL CORPORATION 11 Other BDCS Excl. Non-cash Comp Exp (4)(5)(7) Commercial Banks (8) (1) Total expenses excluding interest expense (2) Based upon the trailing twelve month period ended March 31, 2023 (3) Based upon the trailing twelve month period ended March 31, 2023, excluding non-cash compensation expenses (4) See non-GAAP information disclosures on page 37 and calculation of non-cash compensation expenses on page 39 of this presentation (5) Other BDCs includes dividend paying BDCs that have been publicly-traded for at least two years and have total assets greater than $500 million based on individual SEC Filings as of December 31, 2022; specifically includes: ARCC, BBDC, BCSF, BKCC, CCAP, CGBD, CSWC, FDUS, FSK, GAIN, GBDC, GLAD, GSBD, HRZN, HTGC, MFIC, MRCC, NMFC, OCSL, OFS, ORCC, PFLT, PNNT, PSÉC, PTMN, SAR, SCM, SLRC, TCPC, TPVG, TSLX and WHF NYSE: MAIN (6) Calculation represents the average for the companies included in the group and is based upon the trailing twelve month period ended December 31, 2022 as derived from each company's SEC filings, including non-cash compensation expenses (7) Calculation represents the average for the companies included in the group and is based upon the trailing twelve month period ended December 31, 2022 as derived from each company's SEC filings, excluding non-cash compensation expenses (8) Source: SNL Financial; calculation represents the average for the trailing twelve month period ended December 31, 2022 and includes commercial banks with a market capitalization between $500 million and $3 billion Main Street Capital Corporation mainstcapital.com Page 17#18Stable, Long-Term Leverage - Significant Unused Capacity MAIN maintains a conservative capital structure, with limited overall leverage and an intentional mix of secured, floating rate revolving debt and unsecured, fixed rate long-term debt Capital structure is designed to correlate to and complement the expected duration and fixed/floating rate nature of investment portfolio assets Facility $980.0 million Corporate Facility (1)(3) $255.0 million SPV Facility(2)(3) Notes Payable Notes Payable Notes Payable SBIC Debentures Interest Rate SOFR+1.875% floating (6.6% (4)) SOFR+2.50% floating (7.3%(4)) 3.00% fixed 5.20% fixed 7.74% (5) fixed (weighted average) 2.87% fixed (weighted average) Maturity August 2027(1) MAIN ST CAPITAL CORPORATION November 2027(²) Redeemable at MAIN's option at any time, subject to certain make whole provisions; Matures July 14, 2026 Redeemable at MAIN's option at any time, subject to certain make whole provisions; Matures May 1, 2024 Redeemable at MAIN's option at any time, subject to certain make whole provisions; Matures December 23, 2025 Various dates between 2023 - 2031 (weighted average duration = 5.1 years) Principal Drawn $394.0 million $170.0 million $500.0 million $450.0 million $150.0 million $334.0 million (1) As of March 31, 2023, MAIN maintained a corporate revolving line of credit (the Corporate Facility), which had $980.0 million in total commitments with an accordion feature with the right to request an increase up to $1.4 billion; the Corporate Facility is fully revolving until August 2026, with a maturity date in August 2027 (2) As of March 31, 2023, MAIN maintained a secured special purpose vehicle financing facility (the SPV Facility), which had $255.0 million in total commitments with an accordion feature with the right to request an increase up to $450.0 million; the SPV Facility is fully revolving until November 2025, with a maturity date in November 2027 (3) Borrowings under the Corporate Facility and the SPV Facility (together, the Credit Facilities) are available to provide additional liquidity for investment and operational activities (4) Credit Facilities' rates reflect the rate based on SOFR as of March 31, 2023 and effective as of the contractual reset date as of April 1, 2023 (5) Based upon $100.0 million and $50.0 million in aggregate principal amount bearing interest at 7.84% and 7.53%, respectively Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 18#19Long-term Maturity of Debt Obligations MAIN's conservative capital structure provides long-term access to attractively- priced and structured debt facilities ● Allows for investments in assets with long-term holding periods / illiquid positions and greater yields and overall returns Provides downside protection and liquidity through economic cycles Allows MAIN to be opportunistic during periods of economic uncertainty (in millions) $900 $850 $800 $750 $700 $650 $600 $550 $500 $450 $400 $350 $300 $250 $200 $150 $100 $50 $0 2023 $450.0 $63.8 2024 $150.0 2025 SBIC debentures December 2025 Notes (3) $500.0 2026 $564.0 $75.0 2027 (1) Credit Facilities July 2026 Notes (4) $75.0 2028 2029 MAIN ST CAPITAL CORPORATION May 2024 Notes $35.0 2030 (2) (1) See page 18 for further detail related to MAIN's Credit Facilities (2) Issued in April 2019; with follow-on issuances in December 2019 and July 2020; redeemable at MAIN's option at any time, subject to certain make-whole provisions (3) Issued in December 2022; with a follow-on issuance in February 2023; redeemable at MAIN's option at any time, subject to certain make-whole provisions (4) Issued in January 2021; with a follow-on issuance in October 2021; redeemable at MAIN's option at any time, subject to certain make-whole provisions Main Street Capital Corporation NYSE: MAIN $85.2 2031 mainstcapital.com Page 19#20Interest Rate Impact and Sensitivity MAIN's financial results are subject to impact from changes in interest rates; MAIN's capital structure includes a majority of fixed rate debt obligations, while MAIN's investment portfolio includes a majority of floating rate debt investments with minimum interest rate floors - 72% of MAIN's outstanding debt obligations have fixed interest rates(5), limiting the increase in interest expense - 73% of MAIN's debt investments bear interest at floating rates(5), the majority of which contain contractual minimum index rates, or "interest rate floors" (weighted-average floor of approximately 110 basis points)(6) - Provides MAIN the opportunity to achieve increases in net investment income if market interest rates increase, but also results in reductions to net investment income if market interest rates decrease Main Street Capital Corporation Basis Point Increase (Decrease) in Interes The following table illustrates the approximate annual changes in the components of MAIN's net investment income due to hypothetical increases (decreases) in interest rates(1)(2) (dollars in thousands, except per share data): (100) (75) (50) (25) 25 50 75 100 $ Increase (Decrease) in Interest come (23,523) $ (17,873) (12,223) (6,574) 4,736 10,375 16,025 21,675 (Increase) Decrease in Interest Expense (3) MAIN ST NYSE: MAIN CAPITAL CORPORATION 6,204 $ 4,794 3,384 1,974 (846) (2,256) (3,666) (5,076) Increase (Decrease) in Net Investment Income Increase (Decrease) in Net Investment Income per Share (4) (17,319) $ (13,079) (8,839) (4,600) 3,890 8,119 12,359 16,599 (0.22) (0.16) (0.11) (0.06) 0.05 0.10 0.15 0.21 (1) Assumes no changes in the portfolio investments, outstanding borrowings on the Credit Facilities (as defined on page 18) or other debt obligations existing as March 31, 2023 (2) Assumes that all LIBOR, SOFR and Prime rates would change effective immediately on the first day of the period; however, the actual contractual index rate reset dates will vary in future periods generally on either a monthly or quarterly basis across both our debt investments and our Credit Facilities resulting in a delay in the realization of the increases or decreases in interest income (3) The hypothetical (increase) decrease in interest expense would be impacted by the changes in the amount of debt outstanding under our Credit Facilities, with interest expense (increasing) decreasing as the debt outstanding under our Credit Facilities increases (decreases) (4) Per share amount is calculated using shares outstanding as of March 31, 2023 (5) As of March 31, 2023, based on par (6) Weighted-average interest rate floor calculated based on debt principal balances as of March 31, 2023 Although we believe that this analysis is indicative of the impact of interest rate changes to our net investment income as of March 31, 2023, the analysis does not take into consideration future changes in the credit market, credit quality or other business or economic developments that could affect our net investment income. Accordingly, we can offer no assurances that actual results would not differ materially from the analysis above. mainstcapital.com Page 20#21At-The-Market (ATM) Equity Program ATM Equity Program provides efficient and low cost access to equity capital Provides access to equity capital to match growth of LMM investments on an as- needed basis Provides significant economic cost savings compared to traditional overnight equity offerings Issued equity is accretive to NAV per share Provides permanent capital to match indefinite or long-term holding period for LMM investments Facilitates maintenance of conservative leverage position ● MAIN ST Provides significant benefits vs traditional overnight equity offerings CAPITAL CORPORATION Provides equity capital and liquidity on an as-needed basis, avoiding dilution from larger overnight equity offerings Provides equity capital at significantly lower cost Avoids negative impact to stock price from larger overnight equity offerings (1) Through March 31, 2023 (2) Assumes 6% all-in cost for traditional overnight equity offering Main Street Capital Corporation Raised net proceeds of $869.7 million since inception in 2015 (1) Average sale price is approximately 62% above average NAV per share over same period (1) NYSE: MAIN Resulted in economic cost savings of approximately $43.9 million when compared to traditional overnight equity offering(1)(2) mainstcapital.com Page 21#22LMM Investment Strategy LMM investment strategy differentiates MAIN from its competitors and provides attractive risk- adjusted returns Main Street Capital Corporation Investment Objectives High cash yield from secured debt investments (12.4% weighted- average cash coupon as of March 31, 2023); plus Dividend income, fair value appreciation and periodic capital gains from equity investments ● ● Investments are structured for (i) protection of capital, (ii) high recurring income and (iii) meaningful capital gain opportunity Focus on self-sponsored, "one stop" financing opportunities Partner with business owners, management teams and entrepreneurs Provide highly customized financing solutions • Recapitalization, buyout, growth and acquisition capital ● ● MAIN ST CAPITAL CORPORATION ● ● Extensive network of grass roots referral sources Strong and growing "Main Street" brand recognition / reputation Investments have low correlation to the broader debt and equity markets and attractive risk-adjusted returns NYSE: MAIN mainstcapital.com Page 22#23LMM Investment Opportunity MAIN targets LMM investments in established, profitable companies Characteristics of LMM provide beneficial risk- reward investment opportunities Large and critical portion of U.S. economy 195,000+ domestic LMM businesses(1) ● LMM is under-served from a capital perspective and less competitive MAIN ST CAPITAL CORPORATION Inefficient asset class generates pricing inefficiencies • Typical entry enterprise values between 4.5X-6.5X EBITDA ● Typical entry leverage multiples between 2.0X - 4.0X EBITDA to MAIN debt investment Partner relationship with the management teams of our portfolio companies vs a “commoditized vendor of capital" (1) Source: U.S. Census 2017 - U.S. Data Table by Enterprise Receipt Size; 2017 County Business Patterns and 2017 Economic Census; includes Number of Firms with Enterprise Receipt Size between $10,000,000 and $99,999,999 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 23#24Private Loan Investment Strategy Private Loan portfolio investments are primarily debt investments in privately held companies which have primarily been originated directly by MAIN or to a lesser extent through strategic relationships with other credit funds on a collaborative basis (often referred to in the debt markets as "club deals" because of the small lender group size) MAIN's Private Loan investments are typically made to a company owned by or being acquired by a private equity sponsor Investment Objectives Access proprietary investments with attractive risk-adjusted return characteristics Generate cash yield to support MAIN monthly dividend ● Investment Characteristics Investments in companies that are consistent with the size of companies in our LMM and Middle Market Proprietary investments originated directly by MAIN or through strategic relationships with other investment funds on a collaborative basis ● ● Investments in secured debt investments First lien, senior secured debt investments Floating rate debt investments ● ● MAIN ST CAPITAL CORPORATION Current Private Loan portfolio companies have weighted-average EBITDA of approximately $38.1 million(¹) ● 8% -12% targeted gross yields ● • Weighted-average effective yield of 12.4% (2) ● Net returns positively impacted by lower overhead requirements and modest use of leverage Floating rate debt investments provide matching with MAIN's floating rate Credit Facilities (³) (1) This calculation excludes two Private Loan portfolio companies as EBITDA is not a meaningful metric for these portfolio companies (2) Weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status (3) Includes MAIN's corporate revolving credit facility (the Corporate Facility) and SPV credit facility (the SPV Facility and together with the Corporate Facility, the Credit Facilities); see additional details on page 18 Main Street Capital Corporation mainstcapital.com NYSE: MAIN Page 24#25Middle Market Debt Investment Strategy MAIN maintains a portfolio of debt investments in Middle Market companies Investment Objective • Generate cash yield to support MAIN monthly dividend ● Investments in secured and/or rated debt investments First lien, senior secured debt investments Floating rate debt investments ● MAIN ST Large and critical portion of U.S. economy 220,000+ domestic Middle Market businesses(1) CAPITAL CORPORATION Larger companies than the LMM investment strategy • Current Middle Market portfolio companies have weighted-average EBITDA of approximately $65.4 million ● More relative liquidity than LMM and Private Loan investments 6% - 10% targeted gross yields • Weighted-average effective yield of 11.8% (2) • Net returns positively impacted by lower overhead requirements and modest use of leverage Floating rate debt investments provide matching with MAIN's floating rate Credit Facilities (3) (1) Source: U.S. Census 2017 - U.S. Data Table by Enterprise Receipt Size; 2017 County Business Patterns and 2017 Economic Census; includes Number of Firms with Enterprise Re ipt Size between $10,000,000 and $1,000,000,000 (2) Weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status NYSE: MAIN (3) Includes MAIN's corporate revolving credit facility (the Corporate Facility) and SPV credit facility (the SPV Facility and together with the Corporate Facility, the Credit Facilities); see additional details on page 18 Main Street Capital Corporation mainstcapital.com Page 25#26Asset Management Business MAIN's asset management business represents additional income diversification and the opportunity for greater stakeholder returns MAIN's internally managed operating structure provides MAIN's stakeholders the benefits of this asset management business Growth of asset management business is increasingly driven by MAIN's Private Loan investment strategy MAIN(¹) is the investment adviser to several third party clients in its Asset Management Business ● MAIN(¹) is the investment adviser to and administrator of MSC Income Fund, Inc. (MSIF), a non-listed BDC ● MAIN¹ provides asset management services, including sourcing, diligence and post-investment monitoring MAIN(¹) receives management fees and incentive fees Base management fee of 1.75% of total assets Incentive fees - 20% of net investment income above a hurdle rate and 20% of net realized capital gains MAIN ST MAIN(¹) is the investment adviser and administrator to a private fund and a separately managed account with the investment strategies for these clients solely focused on MAIN's Private Loan investment strategy • CAPITAL CORPORATION Benefits to MAIN No significant increases to MAIN's operating costs to provide services (utilize existing infrastructure and leverage fixed costs and existing investment capabilities) Monetizing the value of MAIN franchise Significant positive impact on MAIN's financial results $8.1 million contribution to net investment income in the first quarter of 2023(²) $22.2 million contribution to net investment income in the year ended December 31, 2022(2) - $103.2 million of cumulative unrealized appreciation as of March 31, 2023 ● ● NYSE: MAIN (1) Through MSC Adviser I, LLC (the External Investment Manager), MAIN's wholly-owned unconsolidated subsidiary (2) Contribution to Net Investment Income includes (a) dividend income received by MAIN from the External Investment Manager and (b) operating expenses allocated from MAIN to the External Investment Manager Main Street Capital Corporation mainstcapital.com Page 26#27Total Investment Portfolio Diversity provides structural protection to investment portfolio, revenue sources, income, cash flows and stakeholder dividends Includes complementary LMM debt and equity investments, Private Loan debt investments and Middle Market debt investments Total investment portfolio at fair value consists of approximately 51% LMM / 36% Private Loan / 7% Middle Market / 6% Other Portfolio(¹) investments ● 195 LMM, Private Loan and Middle Market portfolio companies Average investment size of $18.7 million (²) ● ● ● ● MAIN ST ● CAPITAL CORPORATION ● Significant diversification Issuer Geography Industry End markets Transaction type Vintage Other Portfolio also includes the External Investment Manager and short-term portfolio investments, each as described in MAIN's filings with the Securities Exchange Commission (the SEC) (3) Largest individual portfolio company represents 3.7% of total investment income and 3.1% of total portfolio fair value (most investments are less than 1% of income and fair value) Thirteen non-accrual investments, which represent 0.6% of the total investment portfolio at fair value and 3.2% at cost Weighted-average effective yield of 12.5% (4) ● ● (1) (2) As of March 31, 2023; based on cost (3) Based upon total investment income for the trailing twelve month period ended March 31, 2023 (4) Weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 27#28Portfolio Snapshot - Significant Diversification ($ in millions) Number of Portfolio Companies Lower Middle Market Private Loans Middle Market Other Portfolio External Investment Adviser Total(¹) $ Invested - Cost Basis Lower Middle Market % of Total Private Loans % of Total Middle Market % of Total Other Portfolio % of Total External Investment Adviser % of Total Total(1) 12/31/2020 $ 1,104.6 $ $ $ 70 63 42 12 1 188 $ 43.9 % 769.0 30.6 % 488.9 19.4% 124.7 4.9 % 29.5 1.2 % $ 2,516.7 12/31/2021 $ 1,455.7 73 75 36 13 1 198 $ $ 1,157.5 $ 44.7% 35.5 % 440.9 13.5 % 173.7 5.4 % 29.5 0.9 % $ 3,257.3 12/31/2022 $ 1,719.9 78 85 31 14 1 209 $ $ 1,500.3 $ 45.6 % 39.8 % 401.7 10.7 % 120.4 3.1 % 29.5 0.8 % 3,771.8 3/31/2023 $ 1,727.9 79 86 30 14 1 210 MAIN ST $ 1,527.6 CAPITAL CORPORATION 45.5% 119.7 40.2 % 391.0 10.3 % 3.2 % $ 3,795.7 29.5 0.8 % (1) Excludes MAIN's one short-term portfolio investment of $2.0 million at cost and $1.9 million at fair value as of March 31, 2023 and December 31, 2022 and $2.0 million at cost and fair value as of December 31, 2021; MAIN held no short-term portfolio investments for the period ended December 31, 2020 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 28#29Portfolio Snapshot - Significant Diversification (cont.) ($ in millions) $ Invested - Fair Value Lower Middle Market % of Total Private Loans % of Total Middle Market % of Total Other Portfolio % of Total External Investment Adviser % of Total Total(1) 12/31/2020 $ 1,285.5 $ GA SA % of Total $ Invested in Debt (Cost Basis) Lower Middle Market $ % of Total of Lower Middle Market Private Loans % of Total of Total Private Loans Middle Market % of Total of Total Middle Market Other Portfolio % of Total of Total Other Portfolio External Investment Adviser % of External Investment Adviser Total(1) % of Total Portfolio 47.9 % 740.4 27.6% 445.6 16.6% 96.6 $ 3.5 % 116.8 $ 2,684.9 4.4 % 726.9 65.8 % 721.6 93.8 % 454.6 93.0 % - % - % $ 1,903.1 75.6 % 12/31/2021 $ 1,716.4 48.2 % $1,141.8 32.1 % 395.2 11.1 % 166.1 $ $ $ 4.7% 140.4 3.9 % $ 3,559.9 $ 1,031.9 $ 70.9 % $ 1,107.1 95.7 % 411.4 93.3 % 63.2 36.4 % - $ 2,613.6 % 80.2 % 12/31/2022 $ 2,060.5 $ 1,471.5 $ $ 50.3 % $4,100.3 $ 35.9 % 329.1 8.0 % 116.3 2.8 % 122.9 3.0 % $1,267.7 73.7 % $ 1,457.0 $ 97.1 % 376.9 93.8 % - % - % - $ 3,101.6 82.2 % $ 2,112.6 $ $ MAIN ST CAPITAL CORPORATION $ 1,491.4 $ 3/31/2023 50.8 % $ 35.9 % 306.2 7.4 % 116.1 2.7 % 132.7 3.2 % $ 4,159.0 $ 1,258.8 72.9 % $ 1,483.6 97.1 % 366.1 93.6 % - $ 3,108.5 % % 81.9 % (1) Excludes MAIN's one short-term portfolio investment of $2.0 million at cost and $1.9 million at fair value as of March 31, 2023 and December 31, 2022 and $2.0 million at cost and fair value as of December 31, 2021; MAIN held no short-term portfolio investments for the period ended December 31, 2020 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 29#30Portfolio Snapshot - Significant Diversification (cont.) ($ in millions) 12/31/2020 % of Total $ Invested in Debt that is First Lien (Cost Basis) Lower Middle Market % of Total Lower Middle Market Private Loans % of Total Private Loans Middle Market % of Total Middle Market Other Portfolio % of Total Other Portfolio External Investment Adviser % of External Investment Adviser Total(1) % of Total Portfolio Debt Investments % of Total Investment Portfolio $ 712.6 $ 98.1 % 688.2 95.4 % 420.3 92.4 % - % $ 1,821.1 % 95.7 % 72.4 % $ 1,021.1 12/31/2021 EA $ 1,093.0 GA 99.0 % 98.7 % 406.2 98.7 % - % - % $ 2,520.3 96.4 % 77.3 % $1,256.9 SA 12/31/2022 $ 1,450.6 SA $ 99.1 % 99.6 % 372.3 98.8 % $3,079.8 % % 99.3 % 81.6 % MAIN ST CAPITAL CORPORATION $ 1,248.5 $ 3/31/2023 A $ 1,476.9 99.2 % 99.5 % 363.6 99.3 % - % 1 $ 3,089.0 % 99.3 % 81.3% (1) Excludes MAIN's one short-term portfolio investment of $2.0 million at cost and $1.9 million at fair value as of March 31, 2023 and December 31, 2022 and $2.0 million at cost and fair value as of December 31, 2021; MAIN held no short-term portfolio investments for the period ended December 31, 2020 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 30#31Total Portfolio by Industry (as a Percentage of Cost)(1) ■Intemet Software & Services, 8% Commercial Services & Supplies, 7% ■ Distributors, 5% ■ Professional Services, 5% ■Leisure Equipment & Products, 5% ■ Specialty Retail, 3% ■Tobacco, 3% ■ Media, 2% ■ Computers & Peripherals, 2% Software, 2% ■ Communications Equipment, 2% Auto Components, 2% ■ Electronic Equipment, Instruments & Components, 2% ■Health Care Equipment & Supplies, 1% ■Chemicals, 1% ■Hotels, Restaurants & Leisure, 1% Machinery, 7% Construction & Engineering, 6% ■Health Care Providers & Services, 5% ■Diversified Consumer Services, 5% ■IT Services, 4% ■ Energy Equipment & Services, 3% Containers & Packaging, 3% NYSE: MAIN MAIN ST CAPITAL CORPORATION ■Aerospace & Defense, 2% Building Products, 2% ■Textiles, Apparel & Luxury Goods, 2% ■Diversified Telecommunication Services, 2% Food Products, 2% ■ Diversified Financial Services, 1% ■Intemet & Catalog Retail, 1% ■Food & Staples Retailing, 1% ■ Other, 3% (1) Excluding MAIN's Other Portfolio investments, the External Investment Manager and short-term portfolio investments, each as described in MAIN's filings with the SEC, which in aggregate represent approximately 4% of the total portfolio Main Street Capital Corporation mainstcapital.com Page 31#32Diversified Total Portfolio (as a Percentage of Cost)(1) Invested Capital by Transaction Type LBO/MBO Acquisition 43% 11% 4% Growth Capital 42% Recapitalization/ Refinancing Invested Capital by Geography 29% 20% NYSE: MAIN (2) 17% MAINST CAPITAL CORPORATION 14% 20% (1) Excluding MAIN's Other Portfolio investments, the External Investment Manager and short-term portfolio investments, each as described in MAIN's filings with the SEC, which in aggregate represent approximately 4% of the total portfolio (2) Based upon portfolio company headquarters and excluding any MAIN investments headquartered outside the U.S., which in aggregate represent approximately 2% of the total portfolio Main Street Capital Corporation mainstcapital.com Page 32#33LMM Investment Portfolio LMM investment portfolio consists of a diversified mix of secured debt and lower cost basis equity investments 79 portfolio companies / $2.1 billion in fair value ● 51% of total investment portfolio at fair value Debt yielding 12.6% (¹) (73% of LMM portfolio at cost) 99% of debt investments have first lien position 63% of debt investments earn fixed-rate interest Approximately 830 basis point net cash interest margin vs "matched" fixed interest rate on SBIC debentures and Notes Payable ● Equity ownership in all LMM portfolio companies representing 41% average ownership position (27% of LMM portfolio at cost) Opportunity for dividend income, fair value appreciation and ● ● ● ● MAIN ST CAPITAL CORPORATION ● periodic capital gains 64% of LMM companies (2) with direct equity investment are currently paying dividends Fair value appreciation of equity investments supports Net Asset Value per share growth Lower entry multiple valuations, lower cost basis $384.7 million, or $4.82 per share, of cumulative pre-tax net unrealized appreciation at March 31, 2023 (1) Weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status (2) Includes the LMM companies that (a) MAIN has a direct equity investment and (b) are flow-through entities for tax purposes; based upon dividend income for the trailing twelve month period ended March 31, 2023 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 33#34LMM Investment Portfolio LMM investment portfolio is a pool of high quality, seasoned assets with attractive risk-adjusted return characteristics Median LMM portfolio credit statistics(¹); Senior leverage of 2.9x EBITDA through MAIN debt position 2.6x EBITDA to senior interest coverage Total leverage of 3.1x EBITDA including debt junior in priority to MAIN ● ● ● Average investment size of $26.7 million at fair value or $21.9 million on a cost basis (less than 1% of total investment portfolio) MAIN ST CAPITAL CORPORATION Opportunistic, selective posture toward new investment activity over the economic cycle ● Free cash flow de-leveraging improves credit metrics and increases equity appreciation High quality, seasoned LMM portfolio Total LMM portfolio investments at fair value equals 122% of cost Equity component of LMM portfolio at fair value equals 191% of cost ● ● Significant portion of LMM portfolio has de-leveraged and a majority of the LMM portfolio investments have experienced equity appreciation 50 LMM portfolio companies with unrealized appreciation on equity investments Net unrealized appreciation on LMM Equity investments of $427.2 million (1) These credit statistics exclude portfolio companies on non-accrual and four companies for which EBITDA is not a meaningful metric Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 34#35Private Loan Investment Portfolio Private Loan investment portfolio provides a diversified mix of investments and sources of income to complement the LMM investment portfolio 86 investments / $1.5 billion in fair value 36% of total investment portfolio at fair value ● Average investment size of $17.8 million(¹) (less than 1% of total portfolio) Investments in secured debt instruments 97% of Private Loan portfolio is secured debt 99% of Private Loan debt portfolio is first lien term debt ● ● MAIN ST CAPITAL CORPORATION Debt yielding 12.4% (²) 98%) of Private Loan debt investments bear interest at floating (1) rates(3), providing matching with MAIN's floating rate Credit Facilities (4) ● ● Approximately 525 basis point effective interest margin vs "matched" floating rate on MAIN's Credit Facilities (4) (1) As of March 31, 2023; based on cost (2) Weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status (3) 95% of floating interest rates on Private Loan debt investments are subject to contractual minimum "floor" rates (4) Includes MAIN's Credit Facilities as defined on page 24; see additional details on page 18 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 35#36Middle Market Investment Portfolio Middle Market investment portfolio provides a diversified mix of investments and diverse sources of income to complement the LMM investment portfolio and represents a potential source of liquidity for MAIN's future investment activities 30 investments / $306.2 million in fair value 7% of total investment portfolio at fair value ● Average investment size of $13.0 million(¹) (less than 1% of total portfolio) Investments in secured and/or rated debt investments 94% of Middle Market portfolio is secured debt 99% of Middle Market debt portfolio is first lien term debt ● ● MAIN ST CAPITAL CORPORATION Debt yielding 11.8% (²) 95% (1) of Middle Market debt investments bear interest at floating rates(3), providing matching with MAIN's floating rate Credit Facilities (4) ● ● Over 450 basis point effective interest margin vs "matched" floating rate on MAIN's Credit Facilities (4) (1) As of March 31, 2023; based on cost (2) Weighted-average effective yield is calculated using the applicable interest rate as of March 31, 2023 and includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status (3) 80% of floating interest rates on Middle Market debt investments are subject to contractual minimum "floor" rates (4) Includes MAIN's Credit Facilities as defined on page 24; see additional details on page 18 Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 36#37Non-GAAP Information Distributable net investment income is net investment income as determined in accordance with U.S. Generally Accepted Accounting Principles, or U.S. GAAP, excluding the impacts of non-cash compensation expenses (as defined below). MAIN believes presenting distributable net investment income and the related per share amounts is useful and appropriate supplemental disclosure for analyzing our financial performance since non-cash compensation expenses do not result in a net cash impact to Main Street upon settlement. However, distributable net investment income is a non-U.S. GAAP measure and should not be considered as a replacement for net investment income or other earnings measures presented in accordance with U.S. GAAP and should be reviewed only in connection with such U.S. GAAP measures in analyzing MAIN's financial performance. Non-cash compensation expenses consist of (i) share-based compensation and (ii) deferred compensation expense or benefit, both of which are non-cash in nature. Share-based compensation does not require settlement in cash. Deferred compensation expense or benefit does not result in a net cash impact to Main Street upon settlement. The appreciation (depreciation) in the fair value of deferred compensation plan assets is reflected in Main Street's Consolidated Statements of Operations as unrealized appreciation (depreciation) and an increase (decrease) in compensation expenses, respectively. Main Street believes presenting non-cash compensation expenses is useful and appropriate supplemental disclosure for analyzing its financial performance since non-cash compensation expenses do not result in a net cash impact to Main Street upon settlement. However, non-cash compensation expenses are non-U.S. GAAP measures and should not be considered as a replacement for compensation expenses, total expenses or other earnings measures presented in accordance with U.S. GAAP and should be reviewed only in connection with such U.S. GAAP measures in analyzing Main Street's financial performance. Main Street Capital Corporation MAIN ST CAPITAL CORPORATION Net Debt to NAV Ratio is calculated as the Debt to NAV Ratio as determined in accordance with U.S. GAAP, except that total debt is reduced by cash and cash equivalents. The Non-SBIC Debt to NAV Ratio is calculated in the same manner as the Debt to NAV Ratio, except that outstanding SBIC debentures are excluded from the debt pursuant to an exemptive order MAIN received from the Securities and Exchange Commission. MAIN believes presenting the Net Debt to NAV Ratio is useful and appropriate supplemental disclosure for analyzing its financial position and leverage. MAIN believes presenting the Non-SBIC Debt to NAV Ratio is useful and appropriate supplemental disclosure because Main Street, a business development company, is permitted to exclude such borrowings from its regulatory asset coverage ratio calculation pursuant to an exemptive order received from the Securities and Exchange Commission. However, the Net Debt to NAV Ratio and the Non-SBIC Debt to NAV Ratio are non-U.S. GAAP measures and should not be considered as replacements for the Debt to NAV Ratio and other financial measures presented in accordance with U.S. GAAP. Instead, the Net Debt to NAV Ratio and the Non-SBIC Debt to NAV Ratio should be reviewed only in connection with such U.S. GAAP measures in analyzing MAIN's financial position. NYSE: MAIN mainstcapital.com Page 37#38Main Street Capital Corporation Appendix Main Street Capital Corporation NYSE: MAIN MAIN ST CAPITAL CORPORATION mainstcapital.com Page 38#39MAIN Income Statement Summary ($ in 000's), except per share amounts Total Investment Income Expenses: Interest Expense G&A Expense (2) Distributable Net Investment Income (DNII)(2)(3) DNII Margin % Non-Cash Compensation Expenses (³) Share-based Compensation Expense Deferred Compensation (Expense) Benefit Total Non-Cash Compensation Expenses(³) Net Investment Income Net Realized Gain (Loss) Net Unrealized Appreciation (Depreciation) Income Tax Provision Net Increase in Net Assets Net Investment Income Per Share DNII Per Share (³) Q1 22 79,395 (16,687) (8,054) 54,654 68.8% (2,818) 376 (2,442) 52,212 3,336 14,752 (5,097) $ 65,203 $ $ $ $ 0.73 $ 0.76 $ Q2 22 85,200 (17,295) (10,808) 57,097 67.0% (3,596) 1,225 (2,371) 54,726 $ (5,064) (24,593) (10,320) 14,749 0.75 0.78 $ $ Q3 22 98,387 (21,234) (11,386) 65,767 66.8% $ NYSE: MAIN Q4 22 113,876 (23,060) (10,812) 80,004 70.3% (3,598) (466) (4,064) 75,940 (3,617) 298 (3,319) 62,448 5,031 (5,848) (10,081) (2,060) 55,338 $ 106,315 0.83 $ 0.98 $ 0.88 $ 1.03 $ $ (8,515) 44,738 Positive percentage represents an increase and negative percentage represents a decrease to the Net Increase (Decrease) in Net Assets (2) Excludes non-cash compensation expenses (3) See Non-GAAP Information disclosures on page 37 of this presentation (4) Change in DNII Margin is based upon the basis point difference (increase/(decrease)) NM - Not Measurable / Not Meaningful Main Street Capital Corporation Q1 23 120,254 MAIN ST 85,443 CAPITAL CORPORATION (24,997) (9,814) (4,100) (376) (4,476) 80,967 (28,379) 35,118 (8,114) $ 79,592 1.02 1.07 71.1% Q1 23 vs. Q1 22 Change (¹) 51% (50)% (22)% 56% 225 bps (45)% NM (83)% 55% NM NM NM 22% 40% 41% (4) mainstcapital.com Page 39#40MAIN Per Share Change in Net Asset Value (NAV) ($ per share) Beginning NAV Distributable Net Investment Income(¹) Non-Cash Compensation Expenses (1) Net Realized Gain (Loss) Net Unrealized Appreciation (Depreciation) Income Tax Provision Net Increase in Net Assets Regular Monthly Dividends to Shareholders Supplemental Dividends to Shareholders Accretive Impact of Stock Offerings (²) Other(3) Ending NAV Weighted Average Shares $ Q1 22 25.29 0.76 (0.03) 0.05 0.20 $ (0.07) 0.91 (0.645) (0.08) 0.38 0.03 25.89 $ 71,708,326 Q2 22 25.89 0.78 (0.03) (0.07) (0.34) (0.14) 0.20 (0.645) (0.075) 0.15 (0.15) 25.37 $ 73,304,619 $ Q3 22 NYSE: MAIN 25.37 0.88 (0.05) 0.07 (0.13) (0.03) 0.74 (0.645) (0.1) 0.53 0.05 $ 25.94 $ 75,036,522 Q4 22 MAIN ST 77,802,377 CAPITAL CORPORATION 25.94 1.03 (0.05) (0.12) 0.60 (0.07) 1.39 (0.66) (0.10) 0.20 0.09 26.86 $ Q1 23 26.86 1.07 (0.05) (0.36) 0.44 (0.10) 1.00 (0.68) (0.18) 0.18 0.04 27.23 79,552,200 Certain fluctuations in per share amounts are due to rounding differences between quarters. (1) See Non-GAAP Information disclosures on page 37 and reconciliation of non-cash compensation expenses and DNII per share to Net Investment Income per share on page 39 of this presentation (2) Includes accretive impact of shares issued through the Dividend Reinvestment Plan (DRIP), the At-the-Market (ATM) equity issuance program and the equity offering in August 2022 (3) Includes differences in weighted-average shares utilized for calculating changes in NAV during the period and actual shares outstanding utilized in computing ending NAV and other minor changes Main Street Capital Corporation mainstcapital.com Page 40#41MAIN Balance Sheet Summary ($ in 000's, except per share amounts) LMM Portfolio Investments Private Loan Investments Middle Market Portfolio Investments Other Portfolio Investments External Investment Manager Short-term Investments Cash and Cash Equivalents Other Assets Total Assets Credit Facilities SBIC Debentures Notes Payable (¹) Other Liabilities Net Asset Value (NAV) Total Liabilities and Net Assets Total Portfolio Fair Value as % of Cost $ $ $ $ Q1 22 1,795,456 1,260,664 397,338 102,392 132,920 1,968 17,952 72,293 $ 3,780,983 338,000 343,027 1,133,472 92,830 1,873,654 3,780,983 109 % $ $ Q2 22 $ 3,825,745 $ 44.88 $ 39.94 42.64 1,816,255 $ 1,910,915 1,309,020 1,476,934 363,468 354,286 108,846 117,010 118,320 112,490 1,861 1,855 43,383 61,158 64,592 100,318 3,825,745 $ 4,134,966 $ 4,241,885 380,000 $ 561,000 $ 607,000 343,323 343,618 343,914 1,133,618 1,133,766 1,048,188 103,641 117,162 134,197 1,865,163 1,979,420 2,108,586 109 % 43.65 34.59 38.53 Q3 22 $ NYSE: MAIN 4,134,966 108 % $ 45.28 33.23 33.64 $ Q4 22 2,060,459 1,471,466 329,119 116,299 122,930 1,904 49,121 90,587 Common Stock Price Data: High Close Low Close Quarter End Close (1) Includes $500.0 million of July 2026 Notes, $450.0 million of May 2024 Notes, $185.0 million of December 2022 Notes (repaid Q4 2022) and $150.0 million of December 2025 Notes (100.0 million issued in Q4 2022 and $50.0 million issued in Q1 2023) Main Street Capital Corporation $ $ 4,241,885 $ 109 % 39.50 32.57 36.95 MAIN ST CAPITAL CORPORATION $ Q1 23 2,112,619 1,491,395 306,243 116,067 132,650 1,943 39,752 92,586 4,293,255 564,000 328,206 1,097,435 130,692 2,172,922 4,293,255 110 % 42.49 36.87 36.91 mainstcapital.com Page 41#42MAIN Corporate Data Please visit our website at www.mainstcapital.com for additional information Board of Directors Research Coverage Vincent D. Foster Vilas Abraham & Chairman of the Board Marissa Lobo UBS (212) 713-3241 (212) 713-3922 Main Street Capital Corporation Board of Directors Quanta Services, Inc. J. Kevin Griffin Chief Strategy Officer MaineHealth Dwayne L. Hyzak CEO Main Street Capital Corporation John E. Jackson President & CEO CSI Compressco LP Brian E. Lane CEO & President Comfort Systems USA Dunia A. Shive Board of Directors Dallas News Corporation, Kimberly-Clark Corporation and Trinity Industries, Inc. Stephen B. Solcher Retired CFO BMC Software Executive Officers Dwayne L. Hyzak Chief Executive Officer David L. Magdol President & Chief Investment Officer Jesse E. Morris EVP, Chief Financial Officer & Chief Operating Officer Jason B. Beauvais EVP, General Counsel, Secretary & Chief Compliance Officer Nicholas T. Meserve Managing Director Ryan R. Nelson Vice President & Chief Accounting Officer Main Street Capital Corporation Robert J. Dodd Raymond James (901) 579-4560 Mark Hughes Truist Securities (404) 926-5607 Kenneth S. Lee RBC Capital Markets (212) 905-5995 Mitchel Penn Oppenheimer & Co (212) 667-7136 Bryce Rowe B. Riley Financial (703) 312-1820 Erik Zwick Hovde Group (617) 510-1239 Corporate Headquarters 1300 Post Oak Blvd, 8th Floor Houston, TX 77056 Tel: (713) 350-6000 Fax: (713) 350-6042 Independent Registered Public Accounting Firm Grant Thornton, LLP Houston, TX Corporate Counsel Dechert LLP Washington, D.C. Securities Listing Common Stock - NYSE: MAIN Transfer Agent American Stock Transfer & Trust Co. Tel: (800) 937-5449 www.astfinancial.com NYSE: MAIN MAIN ST CAPITAL CORPORATION Investor Relation Contacts Dwayne L. Hyzak Chief Executive Officer Jesse E. Morris EVP, Chief Financial Officer & Chief Operating Officer Tel: (713) 350-6000 Ken Dennard Zach Vaughan Dennard Lascar Investor Relations Tel: (713) 529-6600 Management Executive Committee Dwayne L. Hyzak, Chief Executive Officer David L. Magdol, President & Chief Investment Officer Jesse E. Morris, EVP, Chief Financial Officer & Chief Operating Officer Jason B. Beauvais, EVP, General Counsel, Secretary & Chief Compliance Officer Investment Committee Dwayne L. Hyzak, Chief Executive Officer David L. Magdol, President & Chief Investment Officer Vincent D. Foster, Chairman of the Board mainstcapital.com Page 42