X0306 4 2020-09-18 0 0001510487 Principia Biopharma Inc. PRNB 0001506218 Hardiman Roy C. C/O PRINCIPIA BIOPHARMA INC. 220 E. GRAND AVENUE SOUTH SAN FRANCISCO CA 94080 0 1 0 0 Chief Business Officer Common Stock 2020-09-18 4 M 0 2758 4.7236 A 120519 D Common Stock 2020-09-18 4 M 0 2242 7.2671 A 122761 D Common Stock 2020-09-18 4 S 0 5000 99.9835 D 117761 D Common Stock 1916 I See footnote Employee Stock Option (right to buy) 4.7236 2020-09-18 4 M 0 2758 0.00 D 2025-02-25 Common Stock 2758 0 D Employee Stock Option (right to buy) 7.2671 2020-09-18 4 M 0 2242 0.00 D 2027-12-13 Common Stock 2242 11519 D The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan. Represents the weighted average sales price per share. The shares sold at prices ranging from $99.95 to $100.05 per share. Upon request by the Commission staff, Issuer, or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. Shares indirectly held by Roy Hardiman, as a fiduciary for his child, of which the Reporting Person may be deemed to share voting and dispositive power over these shares. The stock option is fully vested and immediately exercisable. The stock option vested and became exercisable as to 25% of the shares subject to the option on December 14, 2018, and thereafter vests as to 1/48th of the shares in equal monthly installments, until such time as the option is 100% vested, subject to the continuing employment of the Reporting Person on each vesting date. /s/ Christopher Y. Chai, Attorney-in-Fact for Roy Hardiman 2020-09-22