He has starred in several soap operas, including Guiding Light as Detective Kirk Winters in 1980–1981, Another World as Denny Hobson (1981–1982), General Hospital as Brett Madison (1985–1987), and All My Children as Creed Kelly (1988–1989).
Years later, Horan originated the role of Clay Alden on Loving, playing that part from 1989 to 1991.
Horan had a recurring role in the first two seasons of Star Trek: Enterprise as the enigmatic figure whom fans called "Future Guy".
Horan's television guest appearances include roles on Werewolf, Remington Steele, Zorro, Melrose Place, Lost and Highlander: The Series.
He also provided the voice for the antagonist Skull Face in Metal Gear Solid V: The Phantom Pain.