Marlowe was born Ronald DeLeo in Newark, New Jersey, the son of Emil and Constance Severini Deleo. He had a half-sister, Claudia, and half-brothers Dean and Robert, known as the Guitarist and Bassist of the popular grunge band Stone Temple Pilots. He debuted on television in 1951 on Pulitzer Prize Playhouse (1950–52) in the episode "Hostage" (June 8, 1951) His first feature film role was in the 1954 production of Attila. Two years later, he starred as John Goodwin in an episode "In Summer Promise" on General Electric Theater. He appeared as Jimmy Budd, along with Reagan and his wife Nancy Davis, in the episode "The Long Shadow" in Dick Powell's Zane Grey Theater directed by Budd Boetticher, which aired on January 19, 1961.