Exhibit 5.1

		750 E. PRATT STREET SUITE 900 BALTIMORE, MD 21202 T 410.244.7400 F 410.244.7742 www.Venable.com

July 30, 2025

Blackstone Mortgage Trust, Inc.

345 Park Avenue, 24th Floor

New York, New York 10154

Ladies and Gentlemen:

We have served as Maryland counsel to Blackstone Mortgage Trust, Inc., a Maryland corporation (the “Company”), in connection with certain matters of Maryland law relating to the registration and issuance by the Company of up to 9,966,682 shares (the “Shares”) of class A common stock, par value $0.01 per share (the “Common Stock”), of the Company to be issued from time to time pursuant to the Company’s Dividend Reinvestment and Direct Stock Purchase Plan (the “Plan”), as described in the Prospectus Supplement (as defined below). The Shares are covered by the above-referenced Registration Statement, and all amendments thereto (the “Registration Statement”), filed by the Company with the U.S. Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”).

In connection with our representation of the Company, and as a basis for the opinion hereinafter set forth, we have examined originals, or copies certified or otherwise identified to our satisfaction, of the following documents (hereinafter collectively referred to as the “Documents”):

1. The Registration Statement and the prospectus included therein in the form in which it was transmitted to the Commission under the Securities Act;

2. The Prospectus Supplement, dated July 30, 2025 (the “Prospectus Supplement”), in the form in which it was transmitted to the Commission pursuant to Rule 424(b) under the Securities Act; 6. Resolutions adopted by the Board of Directors of the Company relating to, among other matters, the adoption of the Plan and the registration and issuance of the Shares (the “Resolutions”), certified as of the date hereof by an officer of the Company;

3. The charter of the Company (the “Charter”), certified by the State Department of Assessments and Taxation of Maryland (the “SDAT”);

4. The Seventh Amended and Restated Bylaws of the Company, certified as of the date hereof by an officer of the Company;

5. A certificate of the SDAT as to the good standing of the Company, dated as of a recent date;

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July 30, 2025

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7. The Plan;

8. A certificate executed by an officer of the Company, dated as of the date hereof; and

9. Such other documents and matters as we have deemed necessary or appropriate to express the opinion set forth below, subject to the assumptions, limitations and qualifications stated herein.

In expressing the opinion set forth below, we have assumed the following:

1. Each individual executing any of the Documents, whether on behalf of such individual or another person, is legally competent to do so.

2. Each individual executing any of the Documents on behalf of a party (other than the Company) is duly authorized to do so.

3. Each of the parties (other than the Company) executing any of the Documents has duly and validly executed and delivered each of the Documents to which such party is a signatory, and such party’s obligations set forth therein are legal, valid and binding and are enforceable in accordance with all stated terms.

4. All Documents submitted to us as originals are authentic. The form and content of all Documents submitted to us as unexecuted drafts do not differ in any respect relevant to this opinion from the form and content of such Documents as executed and delivered. All Documents submitted to us as certified or photostatic copies conform to the original documents. All signatures on all Documents are genuine. All public records reviewed or relied upon by us or on our behalf are true and complete. All representations, warranties, statements and information contained in the Documents are true and complete. There has been no oral or written modification of or amendment to any of the Documents, and there has been no waiver of any provision of any of the Documents, by action or omission of the parties or otherwise.

5. The Shares will not be issued or transferred in violation of the restrictions on transfer and ownership contained in Article VII of the Charter.

6. Upon any issuance of Shares, the total number of shares of Common Stock issued and outstanding will not exceed the total number of shares of Common Stock that the Company is then authorized to issue under the Charter.

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Based upon the foregoing, and subject to the assumptions, limitations and qualifications stated herein, it is our opinion that:

1. The Company is a corporation duly incorporated and validly existing under and by virtue of the laws of the State of Maryland and is in good standing with the SDAT.

2. The issuance of the Shares has been duly authorized and, when and if issued and delivered by the Company in accordance with the Resolutions, the Plan and the Registration Statement against payment of the consideration set forth therein, the Shares will be validly issued, fully paid and nonassessable.

The foregoing opinion is limited to the laws of the State of Maryland and we do not express any opinion herein concerning any federal law or the laws of any other state. We express no opinion as to compliance with any federal or state securities laws, including the securities laws of the State of Maryland, or as to federal or state laws regarding fraudulent transfers or the laws, codes or regulations of any municipality or other local jurisdiction. To the extent that any matter as to which our opinion is expressed herein would be governed by the laws of any jurisdiction other than the State of Maryland, we do not express any opinion on such matter. The opinion expressed herein is subject to the effect of any judicial decision which may permit the introduction of parol evidence to modify the terms or the interpretation of agreements.

The opinion expressed herein is limited to the matters specifically set forth herein and no other opinion shall be inferred beyond the matters expressly stated. We assume no obligation to supplement this opinion if any applicable law changes after the date hereof or if we become aware of any fact that might change the opinion expressed herein after the date hereof.

This opinion is being furnished to you for submission to the Commission as an exhibit to the Company’s Current Report on Form 8-K relating to the Shares (the “Current Report”), which is incorporated by reference in the Registration Statement. We hereby consent to the filing of this opinion as an exhibit to the Current Report and the said incorporation by reference and to the use of the name of our firm therein. In giving this consent, we do not admit that we are within the category of persons whose consent is required by Section 7 of the Securities Act.

Very truly yours,

/s/ Venable LLP

Exhibit 5.2

		750 E. PRATT STREET SUITE 900 BALTIMORE, MD 21202 T 410.244.7400 F 410.244.7742 www.Venable.com

July 30, 2025

Blackstone Mortgage Trust, Inc.

345 Park Avenue, 24th Floor

New York, New York 10154

Ladies and Gentlemen:

We have served as Maryland counsel to Blackstone Mortgage Trust, Inc., a Maryland corporation (the “Company”), in connection with certain matters of Maryland law relating to the registration and issuance by the Company from time to time of shares (the “Shares”) of class A common stock, par value $0.01 per share (the “Common Stock”), of the Company having an aggregate sale price of up to $699,069,504 (of which $480,901,049 remains available as of the date hereof). The Shares are covered by the above-referenced Registration Statement, and all amendments thereto (collectively, the “Registration Statement”), filed by the Company with the U.S. Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”).

In connection with our representation of the Company, and as a basis for the opinion hereinafter set forth, we have examined originals, or copies certified or otherwise identified to our satisfaction, of the following documents (hereinafter collectively referred to as the “Documents”):

1. The Registration Statement and the prospectus included therein in the form in which it was transmitted to the Commission under the Securities Act;

2. The Prospectus Supplement, dated July 30, 2025, in the form in which it was transmitted to the Commission pursuant to Rule 424(b) under the Securities Act;

3. The charter of the Company (the “Charter”), certified by the State Department of Assessments and Taxation of Maryland (the “SDAT”);

4. The Seventh Amended and Restated Bylaws of the Company, certified as of the date hereof by an officer of the Company;

5. A certificate of the SDAT as to the good standing of the Company, dated as of a recent date;

6. Resolutions adopted by the Board of Directors of the Company (the “Board”) relating to, among other matters, the registration, sale and issuance of the Shares (the “Resolutions”), certified as of the date hereof by an officer of the Company; 7. A certificate executed by an officer of the Company, dated as of the date hereof; and

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8. Such other documents and matters as we have deemed necessary or appropriate to express the opinion set forth below, subject to the assumptions, limitations and qualifications stated herein.

In expressing the opinion set forth below, we have assumed the following:

1. Each individual executing any of the Documents, whether on behalf of such individual or another person, is legally competent to do so.

2. Each individual executing any of the Documents on behalf of a party (other than the Company) is duly authorized to do so.

3. Each of the parties (other than the Company) executing any of the Documents has duly and validly executed and delivered each of the Documents to which such party is a signatory, and such party’s obligations set forth therein are legal, valid and binding and are enforceable in accordance with all stated terms.

4. All Documents submitted to us as originals are authentic. The form and content of all Documents submitted to us as unexecuted drafts do not differ in any respect relevant to this opinion from the form and content of such Documents as executed and delivered. All Documents submitted to us as certified or photostatic copies conform to the original documents. All signatures on all Documents are genuine. All public records reviewed or relied upon by us or on our behalf are true and complete. All representations, warranties, statements and information contained in the Documents are true and complete. There has been no oral or written modification of or amendment to any of the Documents, and there has been no waiver of any provision of any of the Documents, by action or omission of the parties or otherwise.

5. The Shares will not be issued or transferred in violation of the restrictions on transfer and ownership contained in Article VII of the Charter.

6. Upon the issuance of any Shares, the total number of shares of Common Stock issued and outstanding will not exceed the total number of shares of Common Stock that the Company is then authorized to issue under the Charter.

7. Prior to the issuance of any of the Shares, a duly authorized committee of the Board or officer will determine the price and certain other terms of issuance of such Shares in accordance with the Resolutions (the “Corporate Proceedings”).

Based upon the foregoing, and subject to the assumptions, limitations and qualifications stated herein, it is our opinion that:

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1. The Company is a corporation duly incorporated and validly existing under and by virtue of the laws of the State of Maryland and is in good standing with the SDAT.

2. The issuance of the Shares has been duly authorized and, when issued and delivered by the Company in accordance with the Corporate Proceedings, the Resolutions and the Registration Statement against payment of the consideration set forth therein, the Shares will be validly issued, fully paid and nonassessable.

The foregoing opinion is limited to the laws of the State of Maryland and we do not express any opinion herein concerning any federal law or the laws of any other state. We express no opinion as to compliance with any federal or state securities laws, including the securities laws of the State of Maryland, or as to federal or state laws regarding fraudulent transfers or the laws, codes or regulations of any municipality or other local jurisdiction. To the extent that any matter as to which our opinion is expressed herein would be governed by the laws of any jurisdiction other than the State of Maryland, we do not express any opinion on such matter. The opinion expressed herein is subject to the effect of any judicial decision which may permit the introduction of parol evidence to modify the terms or the interpretation of agreements.

The opinion expressed herein is limited to the matters specifically set forth herein and no other opinion shall be inferred beyond the matters expressly stated. We assume no obligation to supplement this opinion if any applicable law changes after the date hereof or if we become aware of any fact that might change the opinion expressed herein after the date hereof.

This opinion is being furnished to you for submission to the Commission as an exhibit to the Company’s Current Report on Form 8-K relating to the Shares (the “Current Report”), which is incorporated by reference in the Registration Statement. We hereby consent to the filing of this opinion as an exhibit to the Current Report and the said incorporation by reference and to the use of the name of our firm therein. In giving this consent, we do not admit that we are within the category of persons whose consent is required by Section 7 of the Securities Act.

Very truly yours,

/s/ Venable LLP

Exhibit 8.1

July 30, 2025

Blackstone Mortgage Trust, Inc.

345 Park Avenue, 24th Floor

New York, New York 10154

Ladies and Gentlemen:

We have acted as counsel to Blackstone Mortgage Trust, Inc., a Maryland corporation (the “Company”), and BXMT Advisors L.L.C., a Delaware limited liability company (the “Manager”), in connection with the Registration Statement on Form S-3 (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to, among other things, the registration of shares of class A common stock, par value $0.01 per share, of the Company (the “Common Stock”).

We have examined the Registration Statement as it became effective under the Securities Act and the Company’s prospectus dated July 30, 2025 (the “Base Prospectus”), as supplemented by the prospectus supplement dated July 30, 2025 (together with the Base Prospectus, the “Prospectus”) related to the Company’s Dividend Reinvestment and Direct Stock Purchase Plan, filed by the Company pursuant to Rule 424(b) of the rules and regulations of the Commission under the Securities Act, including the documents filed under the Securities Exchange Act of 1934, as amended, that are incorporated by reference in the Prospectus. In such examination, we have assumed the accuracy of the factual matters described in the Registration Statement.

In addition, we have examined, and have relied as to matters of fact upon, originals, or duplicates or certified or conformed copies, of such records, agreements, documents and other instruments and such certificates or comparable documents of public officials and of officers and representatives of the Company and the Manager and have made such other investigations as we have deemed relevant and necessary in connection with the opinion set forth below.

In rendering the opinion set forth below, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies and the authenticity of the originals of such latter documents.

In rendering the opinion set forth below, we have assumed further the accuracy of the representations contained in the officer’s certificate, dated as of the date hereof, provided to us by the Company (the “Officer’s Certificate”). These representations generally relate to the operation and classification of the Company as a real estate investment trust, as defined in Section 856 of the Internal Revenue Code of 1986, as amended. We have not made an independent investigation of the representations set forth in the Officer’s Certificate. For purposes of rendering such opinion, we have also assumed that the Company has been organized and operated and will continue to be organized and operated in the manner described in the Officer’s Certificate, the Registration Statement, the Prospectus and the applicable organizational documents of the Company and that all terms and provisions of such documents have been and will continue to be complied with.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein and in the Prospectus, we are of the opinion that the statements made in the Prospectus under the captions “38. What are the United States federal income tax consequences of participating in the Plan?” and “Material United States Federal Income Tax Considerations,” insofar as they purport to constitute summaries of certain provisions of United States federal income tax law and regulations or legal conclusions with respect thereto, constitute accurate summaries of the matters described therein in all material respects.

We do not express any opinion herein concerning any law other than the federal income tax law of the United States.

We hereby consent to the filing of this opinion letter as Exhibit 8.1 to the Registration Statement and to the use of our name under the caption “Legal Matters” in the Prospectus.