When Beca's father discovers she has not been attending classes, he comes to her with a proposition: if she joins a club and still does not want to remain at college after a year, he will allow it and pay for Beca to move to Los Angeles to pursue the music career. After some persuasion from group leader Chloe Beale, she reluctantly joins the Barden Bellas. Aubrey doesn't initially approve of recruiting Beca, but yields nonetheless due to a desperate need for members and Beca's own talent. Beca joins alongside a group of other women who do not fit the Bellas' typical mold: Cynthia-Rose, Stacie Conrad, Lilly Onakuramara, and Fat Amy. Jesse is also revealed to have joined the Bellas' all-male rival group, the Treblemakers.
The Bellas participate in the southeastern regional competition at Carolina University where, at Aubrey's insistence, they perform the same medley that helped the Bellas advance to the finals the previous year. In spite of their old setlist, the group manages to place second, which gives them the bid to semi-finals. A brief scuffle after the competition leads to Beca's arrest by the police. Jesse tries to help by calling Beca's father, who then tells Beca that he will no longer pay for her to move to Los Angeles. This infuriates Beca which turns her budding friendship with Jesse sour. In the mean time, Beca suggests to the Bellas to try and be more daring, but Aubrey insists that they will win with the repertoire the group has always used in the past.
At the semi-finals, Beca provides an impromptu back-up of one of her favorite songs into the "traditional" song on the Bellas' setlist to reinvigorate the crowd after they seemed to have lost interest. The Bellas come in third in the competition behind the Treblemakers and the Footnotes. Even though the audience seemed to enjoy Beca's remix, Aubrey becomes furious with Beca, who in turn quits the Bellas. When the Footnotes are later disqualified from the national competition because the lead singer was in high school, the Bellas are called to take part in their place. The Bellas get back together after returning from spring break, with the notable exception of Beca. During rehearsals, Chloe has stands up against Aubrey's stubbornness. The group starts to fall apart, which sparks a fight. Meanwhile, Beca tries to apologize to Jesse, which he declines. Beca then apologizes to the Bellas for her actions during the semi-finals and asks to have another chance, which Aubrey eventually allows. After having a group heart-to-heart conversation, the Bellas decide to adopt Beca's more modern and original music style. Meanwhile, group leader Bumper leaves the Treblemakers after being offered a job as a back-up singer for John Mayer. With Bumper gone, Jesse persuades the Trebles to let his previously-rejected roommate Benji join the group in Bumper's place.
At the a cappella national competition, the Bellas sing a piece arranged by Beca, which includes Don't You (Forget About Me) a song featured in Jesse's favorite movie The Breakfast Club. This acts as a more effective apology from Beca, and after the performance, they reunite with a kiss. The Bella's win the national competition and six months later, auditions for new members take place.