Filed pursuant to Rule 497(a)

Registration No. 333-263258

Rule 482ad

[TEXT OF COMMUNICATION SENT VIA BLOOMBERG]

Issuer/Ticker	Main Street Capital Corp (MAIN)
Expected Ratings*	S&P (Exp): BBB-/Stable Fitch (Exp): BBB-/Stable
Format	SEC Registered
Ranking	Sr Unsecured Notes
Tap (Increase)	Yes, MAIN 6.500% 06/04/27
Tap Size	$100mm
Current Amount Outstanding	$300mm
Coupon Type	Fixed
Issue Date	September 11, 2024
Settlement**	T+2 (September 13, 2024)
Maturity Date	June 4, 2027
IPT	T + 215 Area
First Pay	December 4, 2024
Optional Redemption	Make Whole Call: T + 30 until May 4, 2027 Par Call: May 4, 2027
Change of Control	Yes, 100% (See Red)
Cusip	56035LAJ3
ISIN	US56035LAJ35
Active Bookrunner(s)	TSI(B&D), JPM, RBC, SMBC
Use of Proceeds	Repay outstanding debt, including amounts outstanding under Credit Facilities
Sale into Canada	Yes - Exemption
Denominations	2,000 x 1,000
Timing	Today's Business

*Note: A securities rating is not a recommendation to buy, sell or hold securities and may be subject to revision or withdrawal at any time.

**Under Rule 15c6-1 of the Securities Exchange Act of 1934, trades in the secondary market generally are required to settle in one business day, unless the parties to such trade expressly agree otherwise at the time of the trade. Accordingly, purchasers who wish to trade the Notes prior to the date of delivery of the Notes will be required, by virtue of the fact that the Notes initially will settle in two business days (T+2), to specify alternative settlement arrangements to prevent a failed settlement.

Investors are advised to carefully consider the investment objectives, risks, charges and expenses of Main Street Capital Corporation before investing. The issuer has filed a registration statement (including a prospectus and a preliminary

prospectus supplement) with the SEC for the offering to which this communication relates. Before you invest, you should read the preliminary prospectus supplement relating to this offering, together with the accompanying prospectus, filed with the SEC and other documents Main Street Capital Corporation has filed with the SEC for more complete information about Main Street Capital Corporation and this offering. The information in the preliminary prospectus supplement and the accompanying prospectus, and in this announcement, is not complete and may be changed.

You may get these documents for free by visiting EDGAR on the SEC Web site at www.sec.gov. Alternatively, Main Street Capital Corporation, any underwriter or any dealer participating in the offering will arrange to send you the preliminary prospectus supplement if you request it by contacting Truist Securities, Inc., 303 Peachtree Street, Atlanta, Georgia, 30308, Attn: Prospectus Dept, telephone: 800-685-4786, or email: TruistSecurities.prospectus@Truist.com; J.P. Morgan Securities LLC, 383 Madison Avenue, New York, New York 10179, Attn: Investment Grade Syndicate Desk, facsimile: 212-834-6081; RBC Capital Markets LLC, Attention: Investment Grade Syndicate Desk, Brookfield Place, 200 Vesey St., 8th Floor, New York, NY 10281, telephone: 866-375-6829, or e-mail: rbcnyfixedincomeprospectus@rbccm.com; or SMBC Nikko Securities America, Inc., 277 Park Avenue, New York, New York 10172, Attn: Debt Capital Markets, email: prospectus@smbcnikko-si.com;

The preliminary prospectus supplement, the accompanying prospectus and this announcement do not constitute offers to sell or the solicitation of offers to buy nor will there be any sale of the securities referred to in this announcement in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of such state or jurisdiction.

ANY DISCLAIMERS OR OTHER NOTICES THAT MAY APPEAR AFTER THIS MESSAGE ARE NOT APPLICABLE TO THIS COMMUNICATION AND SHOULD BE DISREGARDED. SUCH DISCLAIMERS OR OTHER NOTICES WERE AUTOMATICALLY GENERATED AS A RESULT OF THIS COMMUNICATION BEING SENT VIA BLOOMBERG OR OTHER EMAIL SYSTEM.