His first major acting role was as "Lincoln Hayes" on Aaron Spelling's The Mod Squad. He has guest-starred in television shows such as Hill Street Blues, Miami Vice, The Highwayman, Twin Peaks, Star Trek: Deep Space Nine, Everybody Hates Chris, and in a recurring role as Philby Cross in the Mystery Woman movie series on the Hallmark Channel. He has appeared in films such as Deep Cover, Tales from the Hood, Half Baked, Hoodlum, I'm Gonna Get You Sucka and as jazz great Jelly Roll Morton in "The Legend of 1900", as well as Francis L, the father of Prince's character "The Kid" in the hit movie Purple Rain.
Williams was born in New York City, New York. His grandfather was Clarence Williams, the jazz pianist and composer. He was raised by his grandmother. Williams was married to African-American actress Gloria Foster (The Oracle in The Matrix), who died on September 29, 2001. One of Williams's closest friends is actor Eric Braeden.
Williams's latest portrayal is of Ellsworth Raymond "Bumpy" Johnson (1906–1968) in American Gangster, which was released on November 2, 2007. Johnson was an American gangster in Harlem in the early 20th century. The movie is directed by Ridley Scott. Williams is not listed in the movie credits for the film.