Depp confirmed that he was accepting this part just before the Hollywood premiere of Sweeney Todd: The Demon Barber of Fleet Street.
Universal Pictures offered the part to the 44-year-old actor when they learned that Warner Bros. was postponing the other movie, Shantaram, that Depp was supposed to film in India.
This drama, which takes place between 1933-1934, shows a wave of criminal activity which pushed an FBI agent to try to get gangsters John Dillinger, Baby Face Nelson and Pretty Boy Floyd behind bars.
Depp will play John Dillinger, considered the worst gangster of that time. Mann based his movie on the work by Bryan Burrough, published in 2004. Mann, who also directed Heat and Ali, will start filming in Chicago on March 10.