The Hollywood Reporter said the popular Broadway actor will play Gyp Rosetti, "a charming but ruthless gangster who challenges Nucky," played by Steve Buscemi.
The stars of "Boardwalk Empire" won the Screen Actors Guild Award for Best Ensemble in a Drama Series Sunday, while Buscemi took home the SAG prize for Best Actor in a Drama Series.
Cannavale is best known for his work in the films "The Other Guys," "The Station Agent" and "Shall We Dance?" He had recurring roles on TV's "Nurse Jackie," "Will & Grace," "Third Watch," "Ally McBeal" and "Oz."
He was nominated for a Tony Award for best actor in a play in 2011 for "The Motherf**ker with the Hat" and for best featured actor in a play in 2008 for "Mauritius."