[4] His professional acting career, which spanned more than five decades, included performances in stage plays on and off Broadway, radio dramas, live and filmed episodes of television series, and more than 30 feature motion pictures.

In 1960, Merlin played Travers in Hell Bent for Leather, and his other film credits include roles in Guns of Diablo (1965), The St. Valentine's Day Massacre (1967), Take the Money and Run (1969), The Twilight People (1972), I Escaped from Devil's Island (1973), The Slams (1973), The Hindenburg (1975) and Time Trackers (1989).

Also in 1960 he again died on the screen in season 3, episode 10 of Gene Barry (1919-2009)'s famous Western and historical / biographical television series, Bat Masterson, (1958-1961), playing a wild, gun slinging cowboy, the troubled son of a deceased war hero whose mother left him when he was a child, in the episode "Last Stop To Austin".

Merlin has earlier appeared in a 1954 episode of Dragnet "The Big Rod", cast as Gregory Moore, a felony hit and run suspect.

In 1957, he appeared in Season 1 Episode 21 of Dick Powell's Zane Grey Theatre opposite Ernest Borgnine, also a former US Navy man.

In 1967 Merlin appeared as a hostile alien in episode 18 ("Visitors From Beyond The Stars") of the Irwin Allen sci-fi series The Time Tunnel (1966–1967), and also played a villain on the futuristic nuclear submarine ''U.S.S.

He has also self-published several works of fiction and non-fiction with co-author William Russo, including The Paid Companion of J. Wilkes Booth, Troubles in a Golden Eye, MGM Makes Boys' Town, Hanging with Billy Budd, and Frankie Thomas: the Eternal Cadet.