The actress, who is best known for playing Erin Hannon in the US version of The Office, will play an "annoyingly sincere high school teacher", according to Variety.
21 Jump Street is based on the US television series, which saw two cops forced to go undercover at a high school to fight crime.
Her character will have a crush on Channing Tatum's Jenko, who has been paired with Jonah Hill's socially awkward Schmidt.
Other cast members include Brie Larson (Scott Pilgrim vs. the World) and James Franco's younger brother Dave.
Johnny Depp, who starred in the original programme, will appear in a cameo role in the comedy.
The big-screen adaptation of the US series will mark Hill's directorial debut.
Kemper has previously worked with the comedy actor in Get Him to the Greek.
Watch the trailer to Bridesmaids below: