Seavey competed in his first Iditarod in 1982, and in every race since 1995. In the 1995 race, he started in Seward, and completed the entire length of the Iditarod Trail. He won the 2004 Iditarod in 9 days, 12 hours, 20 minutes, and 22 seconds. He has also won the Copper Basin 300 twice, the Klondike 300, the Kusko 300, and the Grand Portage Passage race in the state of Minnesota once. In 2008 he won the historic All Alaska Sweepstakes race with a record-breaking time of 74 hours, 14 minutes and 37 seconds. .
Seavey was born in Minnesota, and grew up in Seward, Alaska. He lives in Sterling, Alaska with his wife Janine and four sons Dallas, Danny, Tyrell and Conway where they run the Ididaride Sled Dog Tours. Danny has run in the Iditarod, and in the 2005 Iditarod both Tyrell and Dallas competed. Dallas won the 2012 Iditarod, becoming the youngest winner; Mitch became the oldest to win in 2013. In 2015, Mitch and Dallas became the first father and son duo in Iditarod history to claim the top two finishing positions of the race with Dallas arriving at the finish line first and Mitch coming in second.