Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in the following Registration Statements:

(1)Registration Statements (Form S-3 Nos. 333-260292, 333-263455, 333-268524, and 333-276242) and related Prospectuses of Gritstone bio, Inc. (f/k/a Gritstone Oncology, Inc.),

(2)Registration Statements (Form S-8 Nos. 333-230581, 333-237095, 333-254177, 333-255847, 333-263451, 333-264804, and 333-270429) pertaining to the 2018 Incentive Award Plan, the 2018 Employee Stock Purchase Plan, and the 2021 Employment Inducement Incentive Plan, in each case, of Gritstone bio, Inc. (f/k/a Gritstone Oncology, Inc.), and

(3)Registration Statement (Form S-8 No. 333-227665) pertaining to the 2015 Equity Incentive Plan, the 2018 Incentive Award Plan and the 2018 Employee Stock Purchase Plan, in each case, of Gritstone bio, Inc. (f/k/a Gritstone Oncology, Inc.)

of our report dated March 5, 2024, with respect to the consolidated financial statements of Gritstone bio, Inc. included in this Annual Report (Form 10-K) of Gritstone bio, Inc. for the year ended December 31, 2023.

/s/ Ernst & Young LLP

San Mateo, California

March 5, 2024