Seavey, 27, was the first musher under the famed burled arch finish line in Nome. He flew through the last 77 miles to catch the two mushers in front of him, four-time champion Jeff King and Aliy Zirkle, who finished in second.
Seavey finished the race in eight days, 13 hours, 4 minutes and 19 seconds, easily breaking the previous record set in 2011. Zirkle was 2 minutes 22 seconds behind him.
Zirkle also finished second in 2012 and 2013.
King was cruising to a record-tying fifth win when a gust of wind blew him off course, effectively taking him out of the mix just miles from Nome. Until then, he had a safe lead of an hour.
Seavey holds the record for being the youngest champion ever; he was 25 when he won in 2012.
Seavey comes from a mushing family. His grandfather, Dan Seavey, helped organize the first Iditarod in 1973.
His father, Mitch Seavey, has twice won the nearly thousand-mile race across Alaska. Mitch won in 2006 and last year became the race's oldest champion at age 53.
Dallas Seavey was also a champion wrestler. In 2003, he became Alaska's first ever junior champion, winning the 125-pound title.
He's also a participant on the reality television series "Ultimate Survival Alaska."
Seavey admits he's somewhat of a hermit, and doesn't own a television. The only time he sees an episode of the show is when he downloads it on his computer.
"I don't leave my training compound if I can help it," said Dallas. "If I leave, it's by dog team, not by vehicle."
The trail this year has been marked by poor conditions because of a lack of snow after a warm winter by Alaska standards.
A number of mushers were injured at the beginning of the race as their sleds ran on gravel near the Dalzell Gorge. One musher, Scott Janssen of Anchorage, had to be rescued by a National Guard helicopter crew after breaking an ankle.
Snowless conditions again greeted mushers as they reached the western coast of the Alaska.
The race began March 2 in Willow with 69 teams. As of Tuesday morning, 17 mushers had dropped out and one was withdrawn.
The Iditarod winner receives $50,000 and a new truck. The 29 teams after that get cash prizes decreasing on a sliding scale. All other teams finishing the race receive $1,049.
John Baker had held the fastest finish in Iditarod history, covering the trail from Anchorage to Nome in eight days, 18 hours and 46 minutes in 2011.
Hans Gatt of Whitehorse is the top Canadian, sitting in eighth spot. Michelle Phillips of Tagish, Yukon is 19th and Marcelle Fressineau of Whitehorse is 47th.