Richard Donovan, from Galway, ran through wind-chill of minus 25C, snow and ice on Antarctica for 24 hours, 35 minutes and two seconds to set a new record — running 100 miles in a day.
It is the furthest distance anyone has ever covered on foot in one day on the frozen continent.
Two years ago, Donovan ran seven marathons on seven continents in a world record five days, 10 hours and eight minutes.
He suffered only minor injuries in his latest epic endurance test, despite fears of severe frostbite and snow blindness.
“I did feel one of my eyes freeze and I certainly had blurry vision for a short time, but nothing much came of it,” he said.
“I thought I’d have a little snowblindness as my eyes were completely bloodshot at the finish, but nothing developed.
“In fact, my lips and nose appear to be the only body parts showing the physical impact of the cold — they are swollen, scabbed and weather beaten, but will heal in a few days.”
Speaking from the Chilean capital Santiago en route home, Donovan said the real pains did not kick in until 85 miles into the race.
“I actually felt very good until then when accumulated fatigue and a sore hip and knee bothered me, but that was to be expected,” he said.
“I dragged my injured leg around over the remaining distance and felt remarkably well at the end of it.”
Two other competitors in the Antarctic challenge were put on intravenous drips after the race in some of the coldest temperatures on the planet.
Donovan, who has run the length of Ireland in just over five days, dedicated his historic run to his brother Denis, who died suddenly last year.
The polar running expert, who organises both the North Pole and Antarctic Ice Marathons, was the first person in history to run 26 miles at both poles in 2002.