In the military thriller, Penn, 53, is starring as an ex-special forces soldier and military contractor who must chase across Europe in order to clear his name, according to The Hollywood Reporter.
The action thriller will be directed by Pierre Morel, who has previously worked on 'Taken' and 'From Paris with Love'.
Penn most recently appeared on the big screen as a globe-trotting photographer in 'The Secret Life of Walter Mitty'.
'The Gunman' will also star Skyfall's Javier Bardem and Idris Elba, as well as Ray Winstone, Mark Rylance and Jasmine Trinca.