Sepp started out in mountain bike and cross-country ski racing as a junior. He started road cycling while at CU Boulder and went on to win several Collegiate National Championship in mountain bike and road. His first breakout result was a win at the Redlands Classic with other impressive results at the Tour of the Gila. His results earned him a full-season contract with Rally Cycling the following year, having joined the team earlier in 2016. At Rally, he had many impressive results that caught the eye of Jumbo-Visma where he signed his first World Tour contract while he was still in college. Since signing with the team in 2018, he has sky rocketed and become one of the best American talents in the World Tour. Sepp’s career highlights include stage wins in the Tour de France ('21), Vuelta a España ('19), Criterium du Dauphine ('20), and the overall GC at the Tour of Utah ('18).