[1] His brother Geoffrey Deuel was also an actor, best known for his role in Chisum (1970) and numerous episodic television appearances of the 1960s and 1970s; their sister's name was Pamela.

[2] He attended Penfield High School, where he worked on the yearbook staff, campaigned for student government, and was a member of the National Thespians Society.

When his father came to see him in The Rose Tattoo, he realized that his son was only wasting time and money at the university, and told him to follow a career in acting.

After Gidget's cancellation, Duel was quickly offered the starring role of Dave Willis, a newlywed apprentice architect, in the romantic comedy series Love on a Rooftop.

; he also made feature films during this time, beginning with The Hell with Heroes in 1968, playing Rod Taylor’s best friend and co-pilot, Mike Brewer, followed the next year by Generation.

[12] In the early hours of Friday, New Years Eve 1971, Duel died at his Hollywood Hills home of a self-inflicted gunshot wound to the head.

Ray later told police the couple had watched Duel's series Alias Smith and Jones the previous evening.

[18] After his death, his role in Alias Smith and Jones was taken over by Roger Davis, who was previously the narrator over the opening theme of the show.