Thomas began his television career in 1990, playing the role of Kevin Brady, the son of Greg Brady, on The Bradys, a spin-off of the 1970s TV show The Brady Bunch. In 1991, Thomas appeared in three episodes of Fox's sketch comedy series In Living Color. That same year, he was cast as middle son Randy Taylor on ABC's sitcomHome Improvement. Despite looking much younger, in reality, Thomas was a month older than Zachery Ty Bryan who played his elder brother Brad. Thomas remained with Home Improvement well into his teenage years but left the show in 1998 to focus on academics, and was only involved in three episodes of the final season.
On March 22, 2013, Thomas guest-starred on the second-season finale of his third ABC sitcom, Last Man Standing, and again in the fourth episode of the third season on October 11, 2013, reuniting with Tim Allen, his TV father from Home Improvement.[11] On January 10, 2015, he had a small cameo on the twelfth episode of the fourth season of Last Man Standing, reuniting with both of his TV parents from Home Improvement, Tim Allen and Patricia Richardson.[12]
Thomas directed three episodes of Last Man Standing between 2013 and 2016.[13]
Since 2017, Thomas has served as a national board member of the media labor union SAG-AFTRA.[14]
Film
Thomas appeared in many films during and after his run on Home Improvement. He had a few roles as a voice actor in his child years, including Disney's animated feature The Lion King, in which he voiced the protagonist Simba as a cub.