The Borat star has signed up to play villain Monsieur Thenardier in Tom Hooper's upcoming film adaptation of the long-running musical, which also features Hugh Jackman and Russell Crowe.
The comedian is said to have been told that each actor is expected to perform the songs live on camera instead of pre-recording them, which is the usual practice for movie musicals.
"Unlike most film musicals, the cast will record their vocals live on camera rather than go into a studio first then mime on film to the pre-recorded vocal," a source told The Sun.
"It's going to be hard work for Sacha and the rest of the cast. First they have to learn the complex songs, then they'll have to get it right on set in front of the other stars and crew."
Cohen has also signed to star in an upcoming Freddie Mercury biopic.