His life was recorded by a contemporary, the hagiographer Sulpicius Severus. Some of the accounts of his travels may have been interpolated into his vita to validate early sites of his cult. He is best known for the account of his using his military sword to cut his cloak in two, to give half to a beggar clad only in rags in the depth of winter. Conscripted as a soldier into the Roman army, he found the duty incompatible with the Christian faith he had adopted and became an early conscientious objector.
Martin was born in 316 or 336 AD in Savaria in the Diocese of Pannonia (now Szombathely, Hungary). His father was a senior officer (tribune) in the Imperial Horse Guard, a unit of the Roman army, later stationed at Ticinum (now Pavia), in northern Italy, where Martin grew up. The date of his birth is a matter of controversy, with both 316 and 336 having rationales.
At the age of ten he attended the Christian church against the wishes of his parents, and became a catechumen. Christianity had been made a legal religion (in 313) in the Roman Empire. It had many more adherents in the Eastern Empire, whence it had sprung, and was concentrated in cities, brought along the trade routes by converted Jews and Greeks (the term 'pagan' literally means 'country-dweller'). Christianity was far from accepted amongst the higher echelons of society; among members of the army the worship of Mithras would have been stronger. Although the conversion of the Emperor Constantine and the subsequent programme of church-building gave a greater impetus to the spread of the religion, it was still a minority faith.
As the son of a veteran officer, Martin at fifteen was required to join a cavalry ala. At the age of 18 around 334 or 354, he was stationed at Ambianensium civitas or Samarobriva in Gaul (now Amiens, France). It is likely that he joined the Equites catafractarii Ambianenses, a heavy cavalry unit listed in the Notitia Dignitatum. As the unit was stationed at Milan and is also recorded at Trier, it is likely to have been part of the elite cavalry bodyguard of the Emperor, which accompanied him on his travels around the Empire.
According to his biographer, Sulpicius Severus, he served in the military for only another two years, though many scholars believe that these two years, "are in fact not nearly enough to bring the account to the time when he would leave, that is, during his encounter with Caesar Julian (the one who has gone down in history as Julian the Apostate) Martin would have been 45 years old when Julian acceded to the throne, and at the usual end of a military contract. Jacques Fontaine thinks that the biographer was somewhat embarrassed about referring to long stint in the army, ." Such scholars hold that Martin would have remained in the army for the entirety of his prescribed twenty-five year term, and that, in their opinion, such service need not have obliged him to violate his Christian conscience by shedding blood on the battlefield. Regardless of whether or not he remained in the army, Sulpicius Severus reports that just before a battle in the Gallic provinces at Borbetomagus (now Worms, Germany), Martin determined that his switch of allegiance to a new commanding officer (away from antichristian Julian and unto Christ), along with reticence to receive Julian's pay just as Martin was retiring, prohibited his taking the money and continuing to submit to the authority of the former now, telling him, "I am the soldier of Christ: it is not lawful for me to fight." He was charged with cowardice and jailed, but in response to the charge, he volunteered to go unarmed to the front of the troops. His superiors planned to take him up on the offer, but before they could, the invaders sued for peace, the battle never occurred, and Martin was released from military service.