Additional Proxy Soliciting Materials (Form DEFA14A)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

SOLID BIOSCIENCES INC.

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE STOCKHOLDER MEETING TO BE HELD ON JUNE 10, 2026 Your Vote Counts! SOLID BIOSCIENCES INC. 2026 Annual Meeting June 10, 2026 8:00 AM Eastern Time Virtual Meeting Site: www.virtualshareholdermeeting.com/SLDB2026SOLID BIOSCIENCES INC. C/O PROXY SERVICES P.O. BOX 9142 FARMINGDALE, NY 11735 You invested in SOLID BIOSCIENCES INC. and it's time to vote! You have the right to vote on proposals being presented at the Annual Meeting. Get informed before you vote View the Notice and Proxy Statement and Annual Report online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 27, 2026. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to [email protected]. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. For complete information and to vote, visit www.ProxyVote.com Control # Smartphone users Point your camera here and vote without entering a control number Vote in Advance of the Meeting Vote by June 9, 2026 11:59 PM ET Visit www.ProxyVote.com Vote Virtually at the Meeting* June 10, 2026 8:00 AM Eastern Time Visit: www.virtualshareholdermeeting.com/SLDB2026*Please check the meeting materials for any special requirements for meeting attendance.

Vote at www.ProxyVote.com THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. We encourage you to access and review all of the important information contained in the proxy materials before voting. Please follow the instructions on the reverse side to vote these important matters. Voting Items 1. Election of Class II Directors Nominees: 1a. Clare Kahn 1b. Adam Stone 1c. Lynne Sullivan 2. The ratification of the appointment of Ilan Ganot, on an advisory basis, to the Company's Board of Directors as a Class I Director to hold office until the 2028 annual meeting of stockholders. 3. The ratification of the appointment of PricewaterhouseCoopers LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2026. 4. The approval of an amendment to the Company's Certificate of Incorporation, as amended, to increase the number of authorized shares of the Company's common stock from 240,000,000 to 480,000,000. 5. The approval of an advisory vote on executive compensation. NOTE: The proxies are authorized to vote, in their discretion, upon such other business as may properly come before the meeting or any adjournment or postponement thereof. Board Recommends For For For For For For For Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click "Delivery Settings".