Saint Martin was born in Pannonia (A province of the Roman Empire, consisting mostly of modern day Hungary, Austria and Croatia) around 520 AD. At some point in his early life he took a pilgrimage to the Holy Land and became a Monk. Afterwards, on his return home, he met with Spanish Pilgrims who invited him to come to Galicia (Spain) to help convert the Suevi. Saint Martin did so and arrived in Spain in 550 AD.
Once he arrived in Gallica he began at once to convert the Suevi from their mix of Arian and Pagan beliefs, including converting the king Rechiar to Chalcedonian Christianity. He formed several monasteries, most famous of which was at the town of Dumium. At the Synod of Braga in May of 651, he was consecrated as the Bishop of Dumio. Several years later he became the Archbishop of Braga and presided over the second Council of Braga.
Saint Martin was a prolific author and wrote several treaties. Among others he is the author of:
Formula vitae honestae (Rules of an honest life, addressed to the king of Sueves, king Miro.)
De ira (on Anger)
De Correctione rusticorum (the Reform of Rustics)
De trina mersione (On Triple Immersion, addressed to Bishop Boniface where he denounces the arian practice of performing baptism in the three names of the Trinity, rather than triple immresion in the Trinity's single name)
Sententiae Patrum Aegyptiorum (Sayings of the Egyption Fathers)
His De correctione rusticorum contains a catalogue of Iberian pagan practices from the early sixth century. In his monasteries, Saint Martin relaxed the strict discipline of the Desert Fathers to help aid the Iberians in their conversion. Saint Martin also wrote De Pascha, an explanation on how Saint Martin believed the date of Easter should be calculated - never earlier than March 22, no later than April 21, and the date should be announced during Advent so that the laity will know the start of Lent.
Saint Gregory of Tours wrote letters about Saint Martin, praising his piety and great knowledge. He stated that Saint Martin was second to none in his contemporaries of learning
"in tantum se litteris imbuit ut nulli secundus sui temporis haberetur"
Today his feast day is celebrated on March 20th in both the Roman Catholic Church and the Eastern Orthodox Church.