Cera played a fictionalized version of himself in the independent romantic comedy Paper Heart (2009), which followed the fictional relationship between Cera and the film's writer Charlyne Yi, also playing herself. Cera and Yi composed the film's score together. Cera then starred opposite Jack Black in the comedy Year One, set during the Stone Age. The film, directed by Harold Ramis, was poorly received, although Time magazine critic Mary Pols felt Cera's performance saved the film from being a "catastrophe". In his final film of 2009, Cera starred in Youth in Revolt, an adaptation of the eponymous novel. He played a shy teenager named Nick Twisp who creates a destructive alter ego, François Dillinger, after becoming smitten with a girl, who is played by Portia Doubleday. Cera's first published short story, "Pinecone", appeared in McSweeney's Quarterly thirtieth issue. Cera was cast as Scott Pilgrim in the film adaptation of the graphic novel series by Bryan Lee O'Malley after the film's director Edgar Wright had seen Arrested Development and needed an actor "audiences will still follow even when the character is being a bit of an ass". The film, Scott Pilgrim vs. the World, follows Pilgrim, a musician who must battle the seven evil exes of his girlfriend Ramona (played by Mary Elizabeth Winstead). It was released in cinemas in August 2010, whereupon it became a box office bomb after just grossing $47.7 million against a production budget of $85–90 million.
In 2010, Cera contributed mandolin and backing vocals to the Weezer song "Hang On" from their album Hurley. Cera has also established himself as the touring bass player in Mister Heavenly, an indie rock band originating in the American northwest, and is a member of the band The Long Goodbye, along with Clark Duke. Cera also played bass and sang back up during songs in both Scott Pilgrim vs. the World and Nick and Norah's Infinite Playlist. He released his full-length debut album True That on August 8, 2014, through his official Bandcamp page. The album features 19 original tracks, a cover of Roderick Falconer's "Play It Again" as well as a cover of Blaze Foley's "Clay Pigeons."