The competition was established in the 1980s, after two people at the local Neaudd Arms pub bet on whether a man could defeat a horse in a long-distance race.
A group of 1,200 runners competed against 60 horses and riders at the event on June 11, which took place along the cragged hills and muddy terrain of the Welsh countryside.
Lane House Boy came second after Lightfoot with rider Kim Alman, finishing with a time of 2:24:24.
Lightfoot’s stunning performance was even more remarkable given he had been awake since 6 a.m. BST (1 a.m. ET) on Friday in order to fly from Tenerife, Spain to Manchester, UK.
He arrived in Wales at 4 a.m. BST (11 p.m. EST) before travelling to Llanwrtyd Wells on Saturday, just two hours before the race began.
“I am chuffed to have won Whole Earth Man V Horse,” Lightfoot told CNN via email on Monday.
“I’d heard about the two previous winners Huw Lobb and Florien Holtinger, and am delighted to now count myself amongst only three people to have ever beaten the horse.
“It was great to compete in such a legendary, unique race that was all started from a conversation in a local pub. I was awake for 29 hours before the race and had to drive five hours home afterwards, so needless to say I was shattered, but it was worth it,” he added.
A keen endurance runner, Lightfoot previously won the Zegama-Aizkorri race in Spain in 2009.
Three years later he clinched victory after running his first ultramarathon at the Hammer Trail in Denmark, before winning three more endurance trails across Wales, Réunion Island and South Africa in 2013.
In 2014 he came first at the Dodo Trail in Mauritius, and won the Ultra SkyMarathon Madeira the year after.