Hexum was born and raised in Englewood, New Jersey, where he was a musically gifted student at school playing both the horn and the violin in the school orchestra, and even the piano at home. He then attended Case Western Reserve University in Cleveland, Ohio, before transferring across to Michigan State University studying bio-medical engineering and then switching over to philosophy.

While at MSU, Hexum played football, and DJ'd at several local radio stations under the name of "Yukon Jack", before being discovered by John Travolta's manager, Bob LeMond. Hexum allegedly turned down plenty of opportunities to appear in shows such as The Dukes of Hazzard (1979), CHiPs (1977) and many daytime soap operas before finally making his debut in the television series Voyagers! (1982) as time traveler Phineas Bogg. He was then cast as hunk Tyler Burnett alongside Joan Collins in Making of a Male Model (1983), and then as ex-Green Beret Mac Harper in the television series Cover Up: Pilot (1984).