Law's ex-wife, Shawn Ryan, announced his death, the Los Angeles Times reported. She said he died Tuesday at his home in Los Angeles.
No cause of death was disclosed.
Law, the son of a Los Angeles sheriff's deputy and an actress, became interested in acting after taking some classes at the University of Hawaii. He moved to New York and studied with director Elia Kazan at the Lincoln Center Repertory Theater.
Norman Jewison cast Law in his first major role in a U.S. movie, as a Soviet submariner in the 1966 film "The Russians Are Coming, The Russians Are Coming." Two years later, Law played Pygar, an angel who accompanies Fonda around the universe in "Barbarella."
Law had a number of other major roles before starring in "The Love Machine," based on a Jacqueline Susann novel, which became a major flop. He continued to work steadily in both movies and television.