Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the use in this Registration Statement on Form S-1 of our report dated August 24, 2015 relating to the consolidated financial statements of Syndax Pharmaceuticals, Inc. and subsidiaries, appearing in the Prospectus, which is part of this Registration Statement.

We also consent to the reference to us under the heading “Experts” in such Prospectus.

/s/ Deloitte & Touche LLP

Boston, Massachusetts

January 4, 2016