The 37-year-old actor will portray a civilian media adviser to Pitt's four-star US military general, who's trying to win the war in Afghanistan, reported Entertainment Weekly.
Written and directed by David Michod of "Animal Kingdom" fame, "War Machine" is based on Michael Hastings' book "The Operators: The Wild and Terrifying Inside Story of America's War in Afghanistan".
The movie will be produced by Pitt and his Plan B partners Dede Gardner and Jeremy Kleiner, along with Ian Bryce who produced "World War Z".