Timberlake, who has a supporting role in the film that stars Carey Mulligan, teamed up with Mulligan's husband and Mumford & Sons frontman Marcus Mumford for a collaboration on the film's soundtrack.
"OK I can tell you this: There's a Coen brothers film coming out soon that I was lucky enough to work with Oscar Isaac and Carey Mulligan," Timberlake told Capital FM. "And coincidentally I did work with Marcus Mumford on the soundtrack, so I became very good friends with them."
"Marcus and myself, we all kind of worked on the music together. And I don't know any other world where we would have the opportunity to collaborate like that, but it was so much fun. So not only will that be a great movie, but the music to it will be fantastic."
Timberlake returned to making music with "Suit & Tie," his first single since 2007, ahead of the release of a new album, The 20/20 Experience.
Mumford, with T Bone Burnett (O Brother, Where Art Thou?, Crazy Heart), is producing the soundtrack for Inside Llwelyn Davis, a film about a singer-songwriter in 1960's New York, loosely based on Dave Von Ronck's memoir The Mayor of MacDougal Street.
Mumford is coming off a good year, with his group's sophomore album, Babel taking Album of the Year at the Grammys earlier this month.