His career in show business began upon his return to the United States, in 1957, when Sloyan received a scholarship to the American Academy of Dramatic Arts.

[citation needed] Sloyan's television career includes numerous brief performances on daytime dramas The Young and the Restless, General Hospital, and Ryan's Hope, and guest appearances on prime-time series Hawaii Five-O; Wonder Woman; Baywatch; Moonlighting; Quantum Leap; The X-Files; MacGyver; Party of Five; Matlock; Murder, She Wrote; and Dr. Quinn, Medicine Woman.

Sloyan has appeared in a number of science fiction television series, including Buck Rogers in the 25th Century, in which he portrayed Barnard "Barney" Smith in the episode "The Plot to Kill a City", and several roles in the Star Trek franchise.

In Star Trek: The Next Generation, he portrayed Alidar Jarok (a defecting Romulan admiral) in "The Defector", and Alexander Rozhenko (Worf's son) as an adult in the future, in "Firstborn" using the alias "K'mtar".

[citation needed] Sloyan was also a voice actor for Sprint Nextel long-distance services, and in film trailers for movies such as Jumper, The Shadow, and How to Make an American Quilt.