The actor, comedian and "Last Comic Standing" host and executive producer will play Rick the Implausible, a magician.
New Line's movie begins shooting in January. It is about successful Las Vegas magician, Burt Wonderstone, whose partner dies in a risky stunt. After the death, Wonderstone, played by Carell, struggles to rediscover his love for magic and defeat a rival magician.
Don Scardino, who has directed more than 70 episodes of "30 Rock" and many episodes of "Law and Order," "Hope & Faith" and others, is directing.
Jason Reitman wrote the most recent version of the script.
Chris Bender, J.C. Spink, Tyler Mitchell and Jake Weiner are producing.
Mohr played Bob Sugar in 1996's "Jerry Maguire," Marty in 2005's "Are We There Yet?," Sgt. Mike Clady in the 2008 film "Street Kings" and Billy in 2010's "Hereafter."
He also starred as Gary Brooks in the 2010 CBS series "Gary Unmarried."