Jack Denness, of Rochester, will take part in the 60-hour, 135-mile race through California's Nevada desert on 12 July.
The part-time school caretaker has run the race so many times that he has been nicknamed Death Valley Jack.
Runners in the Badwater Ultramarathon face temperatures of up to 55C (130F).
Mr Denness is already the oldest person to have finished the event and has completed it 11 times.
He said: "You have to go through all sorts of stuff, like hallucinations, but it makes it more interesting.
"I'm not an elite runner, I'm just an ordinary bloke who, as it turns out, has been quite successful at running.
"I don't train by the book or run religiously, just when I feel like it."
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I definitely won't do another one - I can't afford to push my luck too much at my age
Mr Denness took up jogging at the age of 45 when he gave up smoking, but has since run more than 150 UK marathons, including 14 London Marathons.
In 2005, he became the first 70-year-old to finish the Badwater Ultramarathon.
He said: "I do it for a challenge. I look around and see that most of the people I went to school with are either dead or seriously ill and think how lucky I am."
Mr Denness said this year's race would be his last.
He said: "I definitely won't do another one. I can't afford to push my luck too much at my age."
Mr Denness has raised more than £100,000 for charity since he began running.
This year he will be raising funds for Kent-based organisation Cerebral Palsy.
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