UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant  ☒                

Filed by a Party other than the Registrant  ☐

Check the appropriate box:

MAGENTA THERAPEUTICS, INC.

(Exact 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):

P.O. BOX 8016, CARY, NC 27512-9903 Magenta Therapeutics, Inc. Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting To Be Held on June 28, 2022 For Stockholders of record as of April 29, 2022 This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. This is not a ballot. You cannot use this notice to vote your shares. We encourage you to access and review all of the important information contained in the proxy materials before voting. To view the proxy materials, and to obtain directions to attend the meeting, go to: www.proxydocs.com/MGTA To vote your proxy while visiting this site, you will need the 12 digit control number in the box below. Under United States Securities and Exchange Commission rules, proxy materials do not have to be delivered in paper. Proxy materials can be distributed by making them available on the internet. The proxy materials available on the Internet include our Proxy Statement and our Annual Report for the fiscal year ended December 31, 2021. For a convenient way to view proxy materials and VOTE go to www.proxydocs.com/MGTA Have the 12 digit control number located in the shaded box above available when you access the website and follow the instructions. If you want to receive a paper or e-mail copy of the proxy material, you must request one. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year’s meeting, you must make this request on or before June 17, 2022. To order paper materials, use one of the following methods. INTERNET www.investorelections.com/MGTA TELEPHONE (866) 648-8133 * E-MAIL paper@investorelections.com When requesting via the Internet or telephone you will need the 12 digit control number located in the shaded box above. * If requesting material by e-mail, please send a blank e-mail with the 12 digit control number (located above) in the subject line. No other requests, instructions OR other inquiries should be included with your e-mail requesting material. Magenta Therapeutics, Inc. Meeting Type: Date: Time: Place: Annual Meeting of Stockholders Tuesday, June 28, 2022 9:00 AM, Eastern Time Annual Meeting to be held live via the Internet - please visit www.proxydocs.com/MGTA for more details. You must register to attend the meeting online and/or participate at www.proxydocs.com/MGTA SEE REVERSE FOR FULL AGENDA

Magenta Therapeutics, Inc. Annual Meeting of Stockholders PROPOSAL 1. To elect two class I directors to our Board of Directors, to serve until the 2025 annual meeting of stockholders and until his or her successor has been duly elected and qualified, or until his or her earlier death, resignation or removal; 1.01 Thomas O. Daniel, M.D. 1.02 Amy Lynn Ronneberg 2. To ratify the appointment of KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2022; and 3. To transact any other business properly brought before the Annual Meeting or any adjournment or postponement of the Annual Meeting. THE BOARD OF DIRECTORS RECOMMENDS A VOTE: FOR THE ELECTION OF THE DIRECTOR NOMINEES LISTED IN PROPOSAL 1 AND FOR PROPOSAL 2