Harold had the lead role of Special Agent Graham Kelton in the short-lived FOX series Vanished in 2006, but his character was killed off in the seventh episode and appeared only as a corpse in the eighth episode.
Harold also guest-starred as Wyatt Earp in two episodes of the HBO series Deadwood and appeared twice on the CBS series The Unit.
Despite his character being killed off in the first season, Harold returned for a guest appearance in the second season of the show in the episode "Put the Damage On" and the executive producer of the show, Kevin Murphy, stated that he plans to bring the character back in season 3 as well if the show gets renewed.
Due to his role as a gay character, Brian Kinney, on Showtime's Queer as Folk, Harold was interviewed by Ilana Rapp for NYCastings about whether the same-sex scenes are a challenge for an actor.
However, the series was cancelled after one season.
Prior to cancellation, however, it was announced that Harold would be a regular in another prospective CW series, The Secret Circle, based on a trilogy of popular young adult novels.
He relocated to Los Angeles and began a 3-year period of intensive drama study.
Gale Harold returned to the New York stage in Tennessee Williams' play Suddenly, Last Summer on November 15, 2006, in the role of Dr. Harold was the male lead in the indie romantic comedy Falling for Grace, which debuted favorably at the 2006 Tribeca Film Festival (under working title East Broadway).
In his theatrical debut, Harold appeared as "Bunny" in Gillian Plowman's Me and My Friends.
In 2000, Harold was cast as Brian Kinney, a central character on Showtime's popular gay drama Queer as Folk.
Among other things, he stated: "I'm straight, but the character was too important to me to muddle his world with my private life. I think it may have helped to introduce Brian as a believable gay man. However it played, it's been out of my hands for a long time".
At the Rise 'n Shine Convention (June 9, 2013), Harold said that he was currently working on a project about Civil War, Field of Lost Shoes.
He was creepy as hell threatening Adam's father (Adam Harrington) and even creepier when he was putting on the nice guy act for Cassie... We already love to hate him." The show would air on the Sy Fy network from April 15, 2013. He sort of walks the line between diplomacy and some of the more hard-knuckled aspects of the world that they’re all in – this post-apocalyptic tribal war zone.