He has described himself as a "momma's boy" and not "the most popular kid" during his school years. Routh has also noted that during his younger years, he was fond of the Superman films and comic books. Routh attended the University of Iowa for a year, aspiring to be a writer.
During this time, he modeled and acted in order to earn his tuition expenses. Routh has said he was often told that he bore a physical resemblance to Christopher Reeve, who had previously portrayed Superman in a film series. His former manager signed him on because of the resemblance, telling him that he thought Routh would be cast as Superman if there were another film in the series. In 1999, Routh left the university and moved to Manhattan and then Los Angeles, where he pursued a full-time acting career, first appearing as an extra in Christina Aguilera's 1999 music video for " What a Girl Wants".
He was cast in his first acting role that same year, in an episode of the short-lived ABC television series Odd Man Out. In 2000, he had a four-episode role on season 3 of MTV's nighttime soap opera Undressed. Routh subsequently appeared on the WB's Gilmore Girls (in a February 2001 episode, "Concert Interruptus", playing a Bangles concert attendee), and earned steady work on the soap opera One Life to Live, playing Seth Anderson from May 23, 2001, until April 17, 2002. Prior to Routh's casting as Superman in the film Superman Returns, Warner Bros.