SUBJECT TO COMPLETION, DATED NOVEMBER 7, 2018 PRELIMINARY PROSPECTUS 7,500,000 SHARES BAIN CAPITAL SPECIALTY FINANCE, INC. Common Stock We are an externally managed specialty finance company focused on lending to middle market companies that has elected to be regulated as a business development company (‘‘BDC’’), under the Investment Company Act of 1940, as amended (together with the rules and regulations promulgated thereunder, the ‘‘1940 Act’’). Our primary focus is capitalizing on opportunities within our Senior Direct Lending strategy, which seeks to provide risk-adjusted returns and current income to our stockholders by investing primarily in middle market companies with between $10.0 million and $150.0 million in annual earnings before interest, taxes, depreciation and amortization. We focus on senior investments with a first or second lien on collateral and strong structures and documentation intended to protect the lender. We may also invest in mezzanine debt and other junior securities, including common and preferred equity, on an opportunistic basis, and in secondary purchases of assets or portfolios, but such investments are not the principal focus of our investment strategy. We are managed by our investment adviser, BCSF Advisors, LP, a subsidiary of Bain Capital Credit, LP. This is an initial public offering of shares of our common stock. All of the shares of common stock offered by this prospectus are being sold by us. Shares of our common stock have no history of public trading. We currently expect that the initial public offering price per share of our common stock will be between $20.25 and $21.25. Our common stock has been approved for listing on the New York Stock Exchange under the symbol ‘‘BCSF’’. BCSF Investments, LLC and certain individuals, including Michael A. Ewald, our Chief Executive Officer and a Managing Director of Bain Capital Credit, Jonathan S. Lavine, Co-Managing Partner of Bain Capital and Founder and Chief Investment Officer of Bain Capital Credit, S IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED. S IN ANY STATE John Connaughton, Co-Managing Partner of Bain Capital, Jeffrey B. Hawkins, Chairman of our Board of Directors and a Managing Director of STATEMENT FILED WITH THE SECURITIES AND EXCHANGE COMMISSION FILED WITH THE SECURITIES AND EXCHANGE STATEMENT Bain Capital Credit, and Michael J. Boyle, our Vice President and Treasurer and a Director of Bain Capital Credit, intend to adopt a 10b5-1 plan (the ‘‘10b5-1 Plan’’) in accordance with Rules 10b5-1 and 10b-18 under the Securities Exchange Act of 1934, as amended (the ‘‘Exchange Act’’). We expect that under such 10b5-1 Plan such parties will buy up to $20 million in the aggregate of our common stock in the open market during the period beginning after four full calendar weeks after the closing of this offering and ending on the earlier of the date on which the capital committed to the 10b5-1 Plan has been exhausted or one year after the closing of this offering, subject to certain conditions. See ‘‘Related Party Transactions and Certain Relationships.’’ Purchases of our common stock in the open market pursuant to the 10b5-1 Plan will be subject to certain conditions and conducted in accordance with Rule 10b-18 under the Exchange Act and other applicable securities laws and regulations that set certain restrictions on the method, timing, price and volume of stock repurchases. We are an ‘‘emerging growth company’’ within the meaning of the Jumpstart Our Business Startups Act (the ‘‘JOBS Act’’). This prospectus contains important information you should know before investing in our common stock. Please read it before you invest and keep it for future reference. We file annual, quarterly and current reports, proxy statements and other information about us with the Securities and Exchange Commission (the ‘‘SEC’’). This information will be available by written or oral request and free of charge by contacting us at Bain Capital Specialty Finance, Inc., 200 Clarendon Street, 37th Floor, Boston, Massachusetts 02116, Attention: Investor Relations, on our website at http://www.baincapitalbdc.com, or by calling us collect at (617) 516-2350. Information contained on our website is not incorporated by reference into this prospectus, and you should not consider that information to be a part of this prospectus. The SEC also maintains a website at http://www.sec.gov that contains this information. Shares of closed-end investment companies that are listed on an exchange, including BDCs, frequently trade at a discount to their net asset value (‘‘NAV’’), per share. If our shares trade at a discount to our NAV, it may increase the risk of loss for purchasers in this offering. Assuming an initial public offering price of $20.75 per share (the mid-point of the estimated initial public offering price range), purchasers in this offering will experience immediate dilution of approximately $0.62 per share. See ‘‘Dilution’’ for more information. Neither the SEC nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. Investing in our common stock involves a high degree of risk, including credit risk and the risk of the use of leverage, and is highly speculative. The securities in which we invest will generally not be rated by any rating agency, and if they were rated, they would be below investment grade. These securities, which may be referred to as ‘‘junk bonds,’’ have predominantly speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal. Before buying any shares of our common stock, you should read the discussion of the material risks of investing in our common stock in ‘‘Risk Factors’’ beginning on page 21 of this prospectus. Per Share Total Public offering price ............................................. $ $ Sales load(1) .................................................. $ $ Proceeds, before expenses, to us(2) .................................... $ $ (1) Our Advisor will pay 50% of the total sales load, which is not reflected in the table above. The portion of the sales load not payable by our Advisor will be borne by us. See ‘‘Underwriting’’ for a more complete description of underwriting compensation. (2) We estimate that we will incur offering expenses of approximately $1,875,000 in connection with this offering (reflecting the 50% of the estimated offering expenses that are payable by us). Our Advisor has agreed to pay 50% of the total estimated offering expenses in connection with this offering. We are not obligated to repay the expenses paid by our Advisor. We have granted the underwriters an option to purchase up to an additional 1,125,000 shares of our common stock from us, at the public offering price, less the sales load payable by us, within 30 days from the date of this prospectus. If the underwriters exercise their option to purchase additional shares in full, the total sales load payable by us will be $ and total proceeds to us, before expenses, will be $ . The shares will be delivered on or about , 2018. Joint Book-Running Managers BofA Merrill Lynch Goldman Sachs & Co. LLC Morgan Stanley Citigroup Credit Suisse Keefe, Bruyette & Woods Wells Fargo Securities A Stifel Company Co-Managers Janney Montgomery Scott JMP Securities Academy Securities IS EFFECTIVE. THIS PROSPECTUS NOT AN OFFER TO SELL THESE SECURITIES AND IT SOLICITING BUY SECURITIE THE INFORMATION IN THIS PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED. WE MAY NOT SELL THESE SECURITIES UNTIL THE REGISTRATION NOT SELL THESE SECURITIES UNTIL THE REGISTRATION BE CHANGED. WE MAY IN THIS PROSPECTUS IS NOT COMPLETE AND MAY THE INFORMATION The date of this prospectus is , 2018. TABLE OF CONTENTS PROSPECTUS SUMMARY .................................................. 1 THE OFFERING .......................................................... 12 FEES AND EXPENSES ..................................................... 18 RISK FACTORS ........................................................... 21 FORWARD-LOOKING STATEMENTS .......................................... 68 USE OF PROCEEDS ....................................................... 70 DISTRIBUTIONS .......................................................... 71 CAPITALIZATION ......................................................... 73 DILUTION............................................................... 74 SELECTED FINANCIAL AND OTHER INFORMATION ........................... 75 MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS ............................................... 77 SENIOR SECURITIES ...................................................... 114 BUSINESS ............................................................... 115 REGULATION ............................................................ 126 MANAGEMENT.......................................................... 133 MANAGEMENT AGREEMENTS ............................................. 145 RELATED PARTY TRANSACTIONS AND CERTAIN RELATIONSHIPS ................ 161 CONTROL PERSONS AND PRINCIPAL STOCKHOLDERS ......................... 163 PORTFOLIO COMPANIES ................................................... 165 DETERMINATION OF NET ASSET VALUE ..................................... 174 DESCRIPTION OF CAPITAL STOCK .......................................... 176 SHARES ELIGIBLE FOR FUTURE SALE ...................................... 182 DIVIDEND REINVESTMENT PLAN