Jornet was born in Sabadell, Catalonia, Spain near Barcelona. He grew up in Refugi de Cap de Rec, a mountain hut at 2000 meters in the Pyrenees at the cross-country Lles ski resort in Lles de Cerdanya, where his father was a hut keeper and mountain guide. At the age of three he climbed Tuc de Molières, a three-thousander in the Pyrenees. By the age of five he climbed Aneto , the highest mountain in the Pyrenees, and a year later he climbed his first four-thousander, the Breithorn () on the Switzerland - Italy border.