Exhibit 5.1

  TELEPHONE: 1-212-558-4000
FACSIMILE: 1-212-558-3588 WWW.SULLCROM.COM 125 Broad Street
New York, New York 10004-2498          LOS ANGELES • PALO ALTO • WASHINGTON, D.C.   BRUSSELS • FRANKFURT • LONDON • PARIS   BEIJING • HONG KONG • TOKYO   MELBOURNE • SYDNEY

June 26, 2025

Bakkt Holdings, Inc.,

10000 Avalon Boulevard, Suite 1000,

Alpharetta, Georgia, 30009.

Ladies and Gentlemen:

In connection with the registration under the Securities Act of 1933 (the “Act”) of 10,339,123 shares of Class A common stock, par value $0.0001 per share (“Class A Common Stock”), of Bakkt Holdings, Inc., a Delaware corporation (the “Company”), issuable upon conversion of the 0% Convertible Debenture due June 18, 2026 issued by the Company (the “Convertible Debenture” and, such shares of Class A Common Stock issuable upon conversion of the Convertible Debenture, the “Securities”), we, as your counsel, have examined such corporate records, certificates and other documents, and such questions of law, as we have considered necessary or appropriate for the purposes of this opinion.

Upon the basis of such examination, it is our opinion that when the registration statement relating to the Securities (the “Registration Statement”) has become effective under the Act and the Securities have been duly issued upon the conversion of the Convertible Debenture in accordance with the terms thereof, the Securities will be validly issued, fully paid and nonassessable.

In rendering the foregoing opinion, we are not passing upon, and assume no responsibility for, any disclosure in any registration statement or any related prospectus or other offering material relating to the offer and sale of the Securities.

The foregoing opinion is limited to the Federal laws of the United States and the General Corporation Law of the State of Delaware, and we are expressing no opinion as to the effect of the laws of any other jurisdiction.

We have relied as to certain factual matters on information obtained from public officials, officers of the Company and other sources believed by us to be responsible.

Bakkt Holdings, Inc. -2-

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to us under the heading “Validity of the Securities” in the prospectus. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act.

Very truly yours,

/s/ SULLIVAN & CROMWELL LLP