Richard Donovan, 42, left yesterday from Mizen Head in Co Cork, the country’s most southerly point, planning to arrive in Donegal’s Malin Head by Friday evening.
He is attempting the 590km feat to raise funds for a Chernobyl Children’s Project programme in Galway.
It intends to bring 46 children to Ireland from the contaminated zones of Belarus in July.
Donovan, who has taken part in so-called ultra-running events all over the world, hopes to do the sprint in less than four days and 12 hours.
That record was set by British athlete Richard Brown 20 years ago.
“There are two reasons for doing it,” Donovan said. “There is a genuine, tough record to be beaten.
“But it is also for Camp Claddagh, an outreach group of the Chernobyl Children’s Project. Usually ultra-running feats capture the public’s imagination, so it’s good to align it with the charity at the same time.”
Bringing the children to Galway is estimated to cost about €45,000. The organisers have managed to raise €26,000.
The Kings Head pub and Malt House Restaurant in Galway is covering the cost of the fundraising venture, which mean all monies raised go to the charity.
Donovan is hoping to cover about 130km, or three full marathons per day.
The economist turned adventure racer is no stranger to such epic feats.
In 2002 he became the first person in the world to run a marathon at both the North and South Poles and has completed races in deserts, the Himalayas and the Amazon Jungle.
“Besides the training I would have done in recent months there is a cumulative effect of having done all those runs in that you learn to manage yourself emotionally and physically,” he said.
“I think it would be difficult and I think it is a bit of a lottery doing these things in that you can get hurt... I’m going into it very determined and hopefully I’ll get there.”
Donovan is also dedicating his world record attempt to his sister-in-law, Fiona Carrick, who died from cancer on March 30 aged just 35.
* More information on www.runthecountry.ie