He is said to have belonged to a branch that ruled Maigh Seóla, although they would not be considered among the Uí Briúin till the 10th century.
He obtained work as chief smith to King Tighernach of Ui Eachach, and in time he gained land at Achaidh Durbchon (near Gougane Barra, source of the river Lee).
They were caught and sentenced to be burned alive for defying Tighernach but in what was regarded as a sign of divine intervention, a storm of heavy rain put out the fire.
When he was seven years old three clerics of Munster, returning from a pilgrimage to Leinster, happened to stop at the house of Amergin.
They admired the boy for the grace of the Holy Spirit that seemed to them to shine in his face, and were allowed by his parents to take him away to be educated.