Exhibit 5.1

[OPINION OF ORRICK, HERRINGTON & SUTCLIFFE LLP]

November 22, 2013

Marcus & Millichap, Inc.

23975 Park Sorrento, Suite 400

Calabasas, California 91302

Ladies and Gentlemen:

We have acted as counsel for Marcus & Millichap, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) of the Company’s Registration Statement on Form S-8 (the “Registration Statement”), under the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration of an aggregate of 5,866,667 shares of the Company’s common stock, par value $0.0001 per share (the “Shares”), reserved for issuance pursuant to the Company’s 2013 Omnibus Equity Incentive Plan (the “EIP”) and its 2013 Employee Stock Purchase Plan (the “ESPP,” and together with the EIP, the “Plans”). As your legal counsel, we have reviewed the actions proposed to be taken by you in connection with the issuance and sale of the Shares to be issued under the Plans.

In connection with this opinion, we have examined originals or copies, certified or otherwise identified to our satisfaction, of (i) the Amended and Restated Certificate of Incorporation of the Company, (ii) the Amended and Restated Bylaws of the Company, (iii) the Registration Statement, (iv) the Plans, and (v) such corporate records, agreements, documents and other instruments, and such certificates or comparable documents of public officials and of officers and representatives of the Company, and have made such inquiries of such officers and representatives, as we have deemed relevant and necessary or appropriate as a basis for the opinion set forth below.

In our examination, we have assumed the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as facsimile, electronic, certified or photostatic copies, and the authenticity of the originals of such copies. In making our examination of documents executed or to be executed, we have assumed that the parties theret