Martin was born around 316 in Pannonia, in what is now Hungary, the son of a Roman military officer, and was enrolled in the cavalry himself as a young man, reportedly against his own wishes since he had already begun leaning toward Christianity. The best known story of his life, recorded by his contemporary biographer Sulpicius Severus, is set during a bitterly cold winter at Amiens in Gaul: Martin, still an unbaptized catechumen serving in the army, encountered a poorly clothed beggar at the city gate, and since he had nothing else to give, cut his own military cloak in two with his sword and gave half to the man. That night, Sulpicius writes, Martin saw Christ in a dream wearing the half cloak he had given away, saying to the surrounding angels that Martin, still only a catechumen, had clothed him.
Martin was baptized soon afterward and eventually left military service, telling the emperor Julian that as a soldier of Christ he was not permitted to fight. He attached himself to Hilary of Poitiers, a leading opponent of Arianism, and around 361 founded a community of hermits at Liguge, considered one of the earliest monastic foundations in Gaul. Sulpicius Severus began circulating this Life while Martin was still alive, an unusual choice that made Martin one of the first non-martyr saints to become widely known through written biography rather than through a cult built up around relics after death, and the account, quickly copied and translated across the Latin West, established a durable literary type, the soldier turned holy man, that later medieval hagiography returned to often.