The Utica, New York, native got his big break when he was cast in Charles Gordone's Pulitzer Prize-winning play No Place to Be Somebody, which began at Off-Broadway's Public Theater and later went to Broadway in 1969. Mr. O'Neal won an Obie Award, Clarence Derwent Award and a Theatre World Award for his work.
The producers of "Superfly," a blaxploitation film, saw him in that production. Impressed, they cast him as the movie's lead character, a cool cocaine dealer named Youngblood Priest.
"Superfly" became an unexpected smash, one of the defining films of the short-lived Blaxploitation genre. Unfortunately, it was also the best known movie of Mr. O'Neal's career, which included many a forgettable, low-budget production.
He returned to Broadway in 1975, replacing Cleavon Little in Murray Schisgal's All Over Town, which was directed by Dustin Hoffman.
He is survived by his wife.