As Thomas got older, he earned a reputation as a teen heartthrob and was a leading cover boy on teen magazines. In 1998, he starred in the Christmas comedy I'll Be Home for Christmas, which, although heavily hyped as his break into movies, was actually a commercial flop. He also appeared in the movies Man of the House, Tom and Huck, Wild America, Common Ground and Speedway Junky. He had a guest role on the ABC sitcom 8 Simple Rules for Dating My Teenage Daughter in early 2004, and appeared in the WB's Smallville in 2003 and 2004. In 2005, he had a guest role in UPN's high school detective drama Veronica Mars, and was also featured on The E! True Hollywood Story's show on Home Improvement.
In 2006, he "appeared" as young Simba (via stock audio from Lion King) in the PlayStation 2 video game Kingdom Hearts II, developed by Square Enix.
Thomas attended Harvard University and the University of St. Andrews in Scotland as a visiting student. He is also a vocal opponent of abortion, and has been very active in various pro-life activities and causes. He has been a strict vegetarian from a young age.