According to the Hollywood Reporter, Pitt had reservations over the political thriller, which tells the story of a team of journalists pursuing the story behind the mysterious death of a political researcher.
Universal has confirmed Pitt's departure but also claimed that it is still "committed to this project".
Dame Helen Mirren and Ed Norton are still expected to star in the movie.
The film is based on the BBC drama series of the same name, which starred Bill Nighy and John Simm.
