According to The Hollywood Reporter, Theroux (Miami Vice, Broken English) will be starring in the comedy along with Danny McBride, James Franco, Natalie Portman and Zooey Deschanel.
The movie is being directed by David Gordon Green (Pineapple Express), and filming is already underway in Ireland.
In other news, Theroux will also be starring in Turkey in the Straw with John Goodman and Paul Rudd. The actor also helped write the screenplays for Tropic Thunder and Iron Man 2, which hits theatres on May 7, 2010.