The Up in the Air actor has co-written the script for The Monuments Men, about a group of art historians and curators who were picked by the U.S. government to retrieve masterpieces stolen from European museums by Nazi thieves.
Clooney will also direct and star in the film, which already has Daniel Craig, Bill Murray and Cate Blanchett attached - and now Damon has signed up for a role.
Confirming recent rumours, he tells E! News, ""Yes, I will be in that movie!""
Clooney's film is based on the book The Monuments Men: Allied Heroes, Nazi Thieves, and the Greatest Treasure Hunt in History by Robert M. Edsel.