Zellweger is engaged in a package deal with Universal and Miramax that will pay her $21 million to do both "Cinderella Man" and the sequel to "Bridget Jones's Diary," which begins filming in October.
In "Cinderella Man," Crowe will play Jim Braddock, a Depression-era boxer who became a folk hero by winning a brutal 15-round match with heavyweight champion Max Baer in 1935. Zellweger will play his wife.
Zellweger has been interested in the role since Crowe first pondered pairing with director Lasse Hallstrom. Since then, the actress turned in a Golden Globe-winning performance for Miramax in "Chicago."
She recently agreed to play Janis Joplin in a biography for Paramount and Lakeshore, and will next be seen starring with Jude Law and Nicole Kidman in the Anthony Minghella-directed adaptation of "Cold Mountain" for Miramax.