In 2000, Mantooth played Ken Crandall in the television movie "Bitter Suite" (original title "Time Share"), and in 2007, he played Dutch Fallon in the television movie "Fire Serpent". Feature film roles include Admiral Edwards in "Agent Red" (2000), Dr. Willis in "He Was a Quiet Man" (2007), Ambassador Cartwright in "Scream of the Bikini" (2009), Richard Cranehill in "Bold Native" (2010), and Detective Bodrogi in "Killer Holiday" (2013). Mantooth also starred on series such as "ER", "Criminal Minds", "Ghost Whisperer", and most recently as Charlie Horse in "Sons of Anarchy" in 2011. Mantooth is marketing a screenplay that focuses on Indian gambling, called "The Bone Game".