Like his brother, Illtud, St. Sadwrn Farchog - the Knight - was probably, sent to school under his great-uncle, St. Garmon (later Bishop of Manaw), in his native Brittany. As a young man, he soon followed in his father, Bican's footsteps and entered the military. Hence his epithet. He married his cousin, St. Canna and together they became the parents of St. Crallo.
Upon retiring from his soldiery, Sadwrn crossed the Channel, with St. Cadfan, and moved his family to South Wales, where his brother was living. He founded the church of Llansadwrn in Caermarthenshire and may have taken leave of his young wife to become a hermit on Anglesey, where he died. The church of Llansadwrn there stands on the site of his little cell and also his grave. As demonstrated by the magnificent 6th century stone, inscribed with his name, which was discovered there in 1742. It now reposes in the internal church wall.
Sadwrn's feast day is 29th November, though this is probably due to being confounded with St. Saturninus of Toulouse. He should not be confused with St. Sadwrn of Henllan who appears in the Life of St. Winifred. In art, Sadwrn of Llansadwrn appears on a tomb in Beaumaris Church as a bearded knight in armour holding a pilgrim's staff and raising his hand in benediction.