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.    )

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☐ Preliminary Proxy Statement

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☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Pursuant to §240.14a-12

BLACKSTONE MORTGAGE TRUST, INC.

(Name of Registrant as Specified In Its Charter)

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

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BLACKSTONE MORTGAGE TRUST, INC. 24TH FLOOR, 345 PARK AVENUE NEW YORK, NY 10154 V14764-P89098 Your Vote Counts! BLACKSTONE MORTGAGE TRUST, INC. 2023 Annual Meeting Vote in advance by June 22, 2023 11:59 PM Eastern Time You invested in BLACKSTONE MORTGAGE TRUST, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the stockholder meeting to be held on June 23, 2023. Get informed before you vote View the Notice and Proxy Statement and Annual Report online at www.ProxyVote.com OR you can receive a free paper or email copy of the material(s) by requesting prior to June 9, 2023. 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 sendmaterial@proxyvote.com. 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 Virtually at the Meeting* June 23, 2023 9:00 AM Eastern Time The Meeting will be held virtually at: www.virtualshareholdermeeting.com/BXMT2023 *To vote these shares during the virtual Meeting, you will need the unique control number indicated above. For instructions on how to attend and participate in the virtual Meeting, visit www.virtualshareholdermeeting.com/BXMT2023. V1.2

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 Board Recommends 1. Election Of Directors Nominees: 01) Michael B. Nash 04) Thomas E. Dobrowski 07) Henry N. Nassau 10) Timothy Johnson For 02) Katharine A. Keenan 05) Martin L. Edelman 08) Jonathan L. Pollack 03) Leonard W. Cotton 06) Nnenna Lynch 09) Lynne B. Sagalyn 2. Ratify the appointment of Deloitte & Touche LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2023. For 3. Advisory Vote on Executive Compensation: To approve in a non-binding, advisory vote, the compensation paid to our named executive officers. For Note: To consider and act upon any other matters which may properly come before the meeting or any adjournment or postponement thereof. Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Delivery Settings”. V14765-P89098