Seavey and 10 dogs crossed the Nome finish line to cheering crowds at 10:39 p.m. Alaska time Tuesday.
"This is for all of the gentlemen of a certain age," he said on a live stream posted to the Iditarod website after completing the race in temperatures just above zero. His race time in the 1,000-mile race was nine days, 7 hours and 39 minutes.
Seavey's victory came after a dueling sprint against Aliy Zirkle, last year's runner-up, along the frozen, wind-whipped Bering Sea coast. Zirkle crossed the finish line 24 minutes after her rival, who greeted her after a while.
"You did a good job," Seavey told Zirkle as a camera crew filmed them. "You're going to win this thing, probably more than once."
At a news conference after the race Zirkle gave credit to her rival's strategy.
"Mitch has this ability to sit on the sidelines and refuel because he knows he needs to refuel, while everyone else is zooming by," she said. "It's smart, and that's probably why you won."
Immediately after finishing, both mushers rushed to pet their dogs, with Seavey singling out his main leader, 6-year-old Tanner, posing for photos with the dog and another leader, Taurus, wearing yellow garlands.
Zirkle's dogs wagged their tails as she praised them. "My dog team is my heart," she said.
The pair jostled for the lead, with Zirkle never more than a few miles behind, in the final stretch.
"I just now stopped looking over my shoulder," Seavey said after winning.
Also trailing by a dozen or so miles was four-time champion Jeff King, who was followed by a cluster of contenders, including Seavey's son, Dallas Seavey. The younger Seavey at age 25 last year became the youngest Iditarod winner ever, beating Zirkle to the finish line by one hour.
Mitch Seavey first won the Iditarod in 2004. Before his Tuesday night win, King had been the oldest Iditarod champion, winning his fourth race at age 50 in 2006.
The oldies were still stellar performers in a race that ended last year with a top field featuring many finishers in their 20s and 30, noted Iditarod race spokeswoman Erin McLarnon.
"Last year, we saw a lot of those youngsters in the top 10," McLarnon said. "Some of those 45-plussers are taking back the lead this year. They are showing the young 'uns what they can really do out there on that trail."
Zirkle, 43, had hoped to be only the third woman to win the race and the first since Susan Butcher won her fourth Iditarod in 1990. Before this year's race, Zirkle noted the long time that had passed since a woman won.
"This is my 13th year, and I've wanted to win every year," she said before the race, which began March 2 with 66 teams at a ceremonial start in Anchorage. The competitive part of the race began the following day in Willow 50 miles to the north. Since then, the race changed leaders several times. Those at the front of the field included four-time champions Lance Mackey and Martin Buser, who later fell behind.
En route to Nome, the race turned into an aggressively contested run among veterans along an often punishing trail.
Conditions on the Yukon River required dogs to go through deep snow and navigate glare ice. Above-freezing temperatures also led to overflow along the trail, a potentially dangerous situation where water has pushed up through the ice and refrozen, creating a weak top layer of ice that teams and mushers can break through.
For reaching Nome first, Seavey wins $50,400 and a new 2013 Dodge Ram pickup truck. The rest of the $600,000 purse will be split among the next 29 mushers to cross the finish line under the famed burled arch on Front Street, a block from the sea.