At the age of two, Walsh began skiing, and by the age of five was ski racing. As an avid athlete, he was also active in the arts and has been acting since the age of six. Since then, he has continued to be involved with acting, music, dance, and numerous other sports, including Nordic ski, hockey and is a triathlon competitor. He was awarded a Junior National Triathlon Championship title at the age of 10. He was diagnosed with Ewing's sarcoma in May 2009 and had his final radiation treatment in June 2010. While recovering from cancer treatments, he attended Green Mountain Valley School and returned to ski racing. After completing his education at GMVS, he enrolled in the Savannah College of Art and Design to get his BFA in Performing Arts and Film Acting, which he completed in 2017. Thomas returned to racing after one year of college and, the following year was invited to be on the U.S. Paralympics Alpine Skiing National Team. Within his first year, he won his first Slalom and Giant Slalom World Cup races. Walsh also earned his MBA in Marketing from DeVry University in 2021. Outside of skiing, his hobbies include the arts, traveling, mountain biking, film, thrifting, and being outdoors. He names Mikaela Shiffrin and Steven Nyman as his idols, and as a cancer survivor, he races for all those who cannot. He credits his mother as the most influential person in his life and career.

Walsh is a two-time Paralympian (2018, 2022), one-time Paralympic medalist (1 silver), and has two bronzes from World Championships in giant slalom and super combined.