Giovanni di Fidanza was born at Bagnoregio in central Italy. As a small child he is said to have been gravely ill and to have been cured by the prayers of St. Francis of Assisi, who exclaimed: 'O buona ventura!' ('O good fortune!') — and the boy took the name as his own.
He joined the new Franciscan order around 1238, studied at Paris under Alexander of Hales, and there became a teaching colleague and intimate friend of his great Dominican counterpart Thomas Aquinas. Elected Minister General of the whole Franciscan Order in 1257 — at just thirty-six — he served in that office for seventeen years through one of the most turbulent periods in the order's history, holding the conventual and spiritual wings together by a combination of personal sanctity, doctrinal clarity, and immense administrative patience.
His writings — the Itinerarium Mentis in Deum ('The Mind's Journey into God'), the Breviloquium, the great commentary on Peter Lombard's Sentences, the Life of St. Francis (the official biography that all earlier Lives were ordered to be destroyed in favour of) — are the central monument of Franciscan theology and of medieval Christian mysticism. He was made Cardinal-Bishop of Albano by Pope Gregory X in 1273; tradition holds that the papal legates found him washing the dishes when they arrived and that he asked them to hang his cardinal's hat on a tree until he was finished.
He died at the Second Council of Lyon in 1274 — having delivered a crucial sermon that secured a brief reunion of the Greek and Latin churches. Aquinas had died on the way to the same council four months earlier.