Samson was born around 490 A.D. in southern Wales. His noble parents were Amon of Dyfed and Anna of Gwynedd.
In his infancy, Samson's parents dedicated him to God and sent him to the monastery of Llantwit Major under the care of St. Illtyd. Samson studied for the priesthood and was ordained in 512 by St. Dubric.
Following his ordination, Fr. Samson retired to a secluded monastery on Caldey Island, of which he was later appointed abbot.
Some Irish monks, returning from a pilgrimage to Rome, sought shelter at Samson's monastery. Samson was so impressed by their holy lives that he accompanied them back to Ireland. He stayed there for some time, during which "he received the submission of an Irish monastery." When he was compelled to return to Wales, Samson sent his uncle to oversee this monastery.
By this time, Samson's fame as a saintly man had spread and he was constantly assailed by his admirers. He, therefore, went, with several other monks, to a secluded place "on the banks of the Severn." However, his devotees soon found him out and compelled him to become abbot of yet another monastery, this one having been formerly by St. Germanus.
He was made a bishop, at the hands of St. Dubric, in 520. Soon after this he was instructed in a vision to evangelize in Brittany. He founded a monastery in Dol which served as his "home base," so to speak, while he was serving in the district. While visiting Paris, at one time, King Childebert nominated Samson for Bishop of Dol.
Samson passed away at Brittany in 565 of natural causes and was buried at Dol.