Item 1.01. Entry Into a Material Definitive Agreement. On February 18, 2025, Solid Biosciences Inc. (the “ Company”) entered into an underwriting agreement (the “ Underwriting Agreement”) with Jefferies LLC and Leerink Partners LLC, as representatives of the several underwriters named therein (collectively, the “ Underwriters”), relating to an underwritten public offering of 35,739,810 shares (the “ Shares”) of the Company’s common stock, par value $0.001 per share (the “ Common Stock”), and, in lieu of Common Stock to certain investors, pre-fundedwarrants (the“ Pre-FundedWarrants”) to purchase 13,888,340 shares of Common Stock (the “ Warrant Shares”). All of the Shares and thePre-FundedWarrants are being sold by the Company. The offering price of the Shares is $4.03 per share and the offering price of thePre-FundedWarrants is $4.029 per share underlying eachPre-FundedWarrant. The Underwriters have agreed to purchase the Shares from the Company pursuant to the Underwriting Agreement at a price of $3.7882 per share and thePre-FundedWarrants from the Company pursuant to the Underwriting Agreement at a price of $3.7872 per share underlying eachPre-FundedWarrant. The closing of the offering is expected to take place on or about February 19, 2025, subject to the satisfaction of customary closing conditions. The Company estimates that the net proceeds from the offering will be approximately $187.5 million, after deducting underwriting discounts and commissions and estimated offering expenses. The Shares and the Pre-FundedWarrants will be issued pursuant to a shelf registration statement on FormS-3(FileNo. 333-277871)that was declared effective by the Securities and Exchange Commission (the “ SEC”) on May 17, 2024. A prospectus supplement relating to the offering has been filed with the SEC.

Item 8.01. Other Events. On February 18, 2025, the Company issued a press release announcing the pricing of the offering. A copy of the press release has been filed as Exhibit 99.1 to this Current Report on Form8-Kand is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits. d) Exhibits Exhibit Description No. 1.1 Underwriting Agreement, dated February 18, 2025, by and among the Company and Jefferies LLC and Leerink Partners LLC ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 4.1 Form of Pre-Funded Warrant 5.1 Opinion of Wilmer Cutler Pickering Hale and Dorr LLP 23.1 Consent of Wilmer Cutler Pickering Hale and Dorr LLP (contained in Exhibit 5.1) 99.1 Press Release dated February 18, 2025 104 Cover Page Interactive Data File (formatted as Inline XBRL) SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. SOLID BIOSCIENCES INC. Date: February 18, 2025 By: /s/ Alexander Cumbo Name: Alexander Cumbo Title: Chief Executive Officer