In 1966–67 season, he appeared as Major Mapoy in all twenty-six episodes of the ABC Western series "The Monroes" with Michael Anderson, Jr., and Barbara Hershey. He appeared in films such as "That Darn Cat!" (1965) as Graham and "The Magic Sword" (1962). Sullivan performed the role of Parmen, a supremely arrogant and cruel telekinetic alien, in the "" episode "Plato's Stepchildren" (1968). He was also featured in the "Twilight Zone" episodes "The Changing of the Guard" and "The Silence". In the latter episode, which aired in 1961, he played a youngish and overly loquacious member of a gentleman's club who accepts a challenging and rather bizarre bet offered by an older member of the club (played by actor Franchot Tone) which ends in unintended, classic Twilight Zone consequences. In the former episode, which aired a year later in 1962, Sullivan played the headmaster of a private boarding school who must deliver the bad news to an "aging out" teacher, played by Donald Pleasence.