At age 25, Seavey became the youngest musher ever to win the Iditarod, winning the 2012 Iditarod in 9 days, 4 hours, 29 minutes, 26 seconds. He is the son of 2004 and 2013 Iditarod champion Mitch Seavey. His grandfather, Dan Seavey, is also a veteran Iditarod musher, having competed in the first two Iditarod sled dog races in 1973 and 1974, in addition to the 1997 and 2012 races.
In 2014, Dallas Seavey won his second Iditarod, completing the race less than two minutes ahead of second place finisher Aliy Zirkle, with a record fast finish time of 8 days, 13 hours 4 minutes and 19 seconds. Seavey's 2014 finish time broke the previous record of 2011 winner John Baker by more than five hours.
Dallas Seavey appeared in two seasons of Ultimate Survival Alaska. On Season Two, Dallas was on the winning team. Next, he will compete against his father in an Ultimate Alaskan Survival- Seavey vs. Seavey.