Izzard, 54, completed his final 26.2-mile run at the feet of a large statue of former South African President Nelson Mandela, in whose honor the challenge is structured. (He ran one marathon each day for every year Mandela was imprisoned.)
Izzard's efforts raised more than $1 million for this year's Sport Relief, according to the BBC, a biennial charity effort.
At the run's end, Izzard was at a literal loss for words (and almost out of breath) as he spoke to the BBC, at one point breaking into tears.
"Thank you. It's been the hardest thing I've ever done. I'm very tired," he said. "So thank you for everyone who's donated. This was tough. So don't do this at home. I don't know if I can say much more."
An unscheduled rest day early in the challenge meant Izzard had to run two marathons on Sunday, the final day, according to the BBC.
In the course of running 707 miles, Izzard overcame dehydration, heat exhaustion and sunstroke, according to the BBC.
End of first marathon day27Posted by Eddie Izzard on Sunday, March 20, 2016
His marathons complete, Izzard celebrated Sunday with a bottle of sparkling wine, according to the BBC – from which he took one long drink, straight from the bottle.