The Spaniard completed the ascent and descent of the 4,810-metre peak in 4 hours, 57 minutes and 40 seconds, knocking 13 minutes of a 23-year-old record along the way.
Even more impressively, he bounded up and down the dangerous mountain dressed only in a t-shirt, shorts and trainers.
Jornet, 25, took off from the town of Chamonix, which lies 1,037 metres above sea level, at 4.46am.
It took him just 3 hours 30 minutes to summit the peak.
With him was Mathéo Jacquemond, but sadly the 22-year-old Frenchman was injured on the way down, which mean Jornet was left to make a triumphant return alone, arriving back at church at 9.43am.
“The snow conditions were good, so we were able to descend easily, by sliding down on our bottoms or running,” the extreme athlete said on his return. “It was a shame to finish alone. I did the entire ascent and the descent with Matteo.
"I think the record is for both of us even if I am the only one to make it back to the church.”
Jornet is not going to stop at Mont Blanc, however, and plans to set records for climbing eight other mountains, including Mount Elbrus (5,642 metres) in Russia, and the Matterhorn (4,478 metres) in the Alps.
He also has his eye on the biggest mountain of them all, Mount Everest, where the current record stands at 20 hours and 24 minutes.
(Photo: Killian Jornet stops to refuel in the Mafate circus during the 20th Diagonale des Fous, or Grand Raid, a 170-km run across La Reunion, in October 2012)
Ben McPartland/The Local