The actor, who is currently starring in Easter-themed Hop and a remake of Dudley Moore's Arthur, has been rumoured for a part in the big-screen version of the Broadway stage show for months.
This afternoon, director Adam Shankman tweeted: "I can officially announce Russell Brand as your Lonny in #rockofagesmovie ! I see a mullet in his future...maybe a Nikki Six? (sic)"
Brand will take the role of rock club promoter and narrator Lonny and joins Tom Cruise, who will portray rock star Stacee Jaxx, in the stage show adaptation.
Paul Giamatti and Amy Adams are also thought to have signed for the project, which is a love story told through 1980s metal anthems by Bon Jovi, Journey and Poison, among others.