Rapper-actor Mos Def (AKA Yasiin Bey) is joining several other musician-turned-thespians in the upcoming music drama "Can a Song Save Your Life?," from "Once" helmer John Carney.

The film already boasts a stellar cast, including Keira Knightley, Mark Ruffalo, and Hailee Steinfeld, plus Maroon 5 singer Adam Levine and Gnarls Barkley/Goodie Mob frontman Cee-Lo Green. The latter two both appear on NBC's hit reality show "The Voice."

Judd Apatow is exec producing the drama in which a young woman (Knightley) re-locates to New York to pursue her music dreams, only to immediately be dumped by her musician boyfriend (Levine). She them happens upon a washed-up record producer (Ruffalo), and the two are able to save each other's creative lives.

According to The Hollywood Reporter, Mos Def will play Ruffalo's producing partner. The actor was recently seen on "Dexter."