[3] He was known for playing the role of Deputy Marshal Heck Martin in the first season of the American western television series Outlaws.

[5] Gaynor began his acting career in 1960, joining the cast of western television series Outlaws for its first season as Deputy Marshal Heck Martin.

[1] He was not liked by other cast members, his character did not appeal to the viewers,[1] and he only appeared in nine episodes before being replaced by Wynn Pearce.

[6][3] Gaynor continued appearing in television programs, with his credits including Voyage to the Bottom of the Sea, Rawhide (1961) – Ogalla in S3:E15, "Incident of the Fish Out of Water" & in S4:E18, "The Deserters’ Patrol", Mission: Impossible, Batman, The Life and Legend of Wyatt Earp, The Invaders, Iron Horse, Coronet Blue and Colt .45.

[3] Gaynor also played the recurring role of Dr. William Scott in the television soap opera The Doctors.