From 1991 to 1999, Thomas starred along side comedian Tim Allen on the ABC sitcom Home Improvement. He played Tim Taylor's second son, Randy, but later left the show to focus on academics.
He voiced young Simba in the The Lion King. Archival recordings of his work were used in later Lion King media when young Simba's voice was needed.
He also was the first of three (at their respective times) boys to voice Spot the Dog in the American dub of the British children's series of the same name, the second being Ryan O'Donohue and the third being Haley Joel Osment.
In 2005, he voiced Shizokuti in the English version of Pom Poko.
In 2013, he played John Baker in 3 episodes of Last Man Standing, reuniting with Tim Allen, his on-screen father from Home Improvement. In 2015, he starred in one episode of Last Man Standing as Randy, reuniting with his TV parents Tim Allen and Patricia Richardson.