Son of current USA Rugby Boys High School All-American Head Coach Salty Thompson, Brett began playing rugby at the age of 12. He was recruited to the University of Arizona to walk on to the football team and played for two years before switching to rugby full-time. Thompson scored a try against rival Arizona State to lead the Wildcats to the 2010 National Collegiate Championship and scored his first for the Eagles on his 15s debut against Canada in Sacramento, California, in June 2014.