Exhibit 5.1

September 9, 2020

StepStone Group Inc.

450 Lexington Avenue, 31^st Floor

New York, New York 10017

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-1, File No. 333-248313, as amended (the “Registration Statement”), of StepStone Group Inc., a Delaware corporation (the “Company”), filed with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), in connection with the offering by the Company of up to 20,125,000 shares of the Company’s Class A common stock, par value $0.001 per share, (the “Shares”). The Shares include shares which may be purchased by the underwriters upon the exercise of the option to purchase additional Shares.

In arriving at the opinion expressed below, we have examined originals, or copies certified or otherwise identified to our satisfaction as being true and complete copies of the originals, of specimen Common Stock certificates and such other documents, corporate records, certificates of officers of the Company and of public officials and other instruments as we have deemed necessary or advisable to enable us to render the opinions set forth below. In our examination, we have assumed without independent investigation the genuineness of all signatures, the legal capacity and competency of all natural persons, the authenticity of all documents submitted to us as originals and the conformity to original documents of all documents submitted to us as copies.

Based upon the foregoing, and subject to the assumptions, exceptions, qualifications and limitations set forth herein, we are of the opinion that when the Registration Statement has become effective under the Securities Act and the Company’s certificate of incorporation substantially in the form filed as an exhibit to the Registration Statement has been duly filed with the Secretary of State of the State of Delaware, the terms of the sale of the Shares have been duly established in conformity with the Company’s certificate of incorporation, and the Shares have been duly issued and sold as contemplated by the Registration Statement, the Shares will be validly issued, fully paid and non-assessable.

September 9, 2020

Page 2

We consent to the filing of this opinion as an exhibit to the Registration Statement, and we further consent to the use of our name under the caption “Validity of the Class A Common Stock” in the Registration Statement and the prospectus that forms a part thereof. In giving these consents, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the Rules and Regulations of the Commission.

Very truly yours,

Sincerely,

/s/ Gibson, Dunn & Crutcher LLP