The Boardwalk Empire actor will play hip-hop star Ol' Dirty Bastard, aka Russell Jones.
According to The Hollywood Reporter, the film will centre on the years leading up to Jones's death from a drug overdose, and specifically his relationship with young intern-turned-manager Jarred Weisfeld, who engineered his comeback.
Jones, a co-founder of influential hip-hop collective the Wu-Tang Clan, famously struggled with addiction and had spent time in prison prior to his death in 2004.
Debut director Joaquin Baca-Asay will helm the film, with Beginners producers Lars Knudsen and Jay Van Hoy producing.
Williams is best known for playing Chalky White in Boardwalk Empire and Omar Little in The Wire. He has also guest-starred on NBC's Community.