Barfoot, of Auckland, spent 18 hours and eight minutes swimming, biking and running his way through the 226km Challenge Wanaka course, setting off at 6.30am on Saturday and crossing the finish line in last place before a huge crowd of cheering spectators at 12.38am on Sunday.
While the official cut-off time was 11.30pm, officials kept the course open for Barfoot to complete the race.
Most Ironman events have a strict completion time limit of 17 hours, but "Challenge have got a bit more heart", Barfoot told the Otago Daily Times yesterday.
"And the thing with Garth is even if you try to take him off the course, he won't go," race director Victoria Murray-Orr said.
Barfoot started running long distance races when he was 50 and in the past 25 years has competed at events all over the world. Saturday's race was the 28th iron distance triathlon race he has started and the 19th he has finished.
Yesterday, he was back at the office in Auckland where he still works four days a week, feeling fit as a fiddle.
"I never felt miserable," he said of his race.
Because he had failed to complete the last three international iron distance triathlons he had entered, he was determined to finish on Saturday so his family would not try and talk him into retiring from the long distance circuit.
"I was pretty pleased in the sense that I didn't push myself too hard because I knew that they [race officials] weren't going to enforce the conventional rules too rigidly.
"I wondered whether they were sort of altering the rules especially for me, but I didn't ask."
Barfoot said he got a "terrific lift" when he managed to overtake three cyclists on the bike leg of the race.
"They got their revenge of course and overtook me on the run."
Barfoot is a director of real estate firm Barfoot and Thompson, which is a sponsor of Challenge Wanaka. He has competed either as an individual or as part of a team in every Challenge Wanaka since the event began in 2007.
Despite Barfoot's late finish, a small contingent of people ran the last kilometre with him and there were still hundreds of supporters forming a human welcome arch for him down the finishing shute on Ardmore St.
