A monk of Iona and successor of Aidan at Lindisfarne
Fionán was Irish by birth and became a monk of Iona. He may have gone with St Aidan to Lindisfarne and became his successor as abbot there in 651. He staunchly upheld Celtic traditions especially as regards the date of Easter.

He built a wooden church on Lindisfarne, constructed of oak, with a roof 'thatched with reeds after the Irish manner'. It seems that Aidan's other-worldliness had been so great (and perhaps his link with Oswald so strong) that he had not embarked on this task. It must have become increasingly necessary for the monks to have a place of worship of their own during Oswy's reign, when the Lindisfarne monks no longer had the same close link with the king, and the queen Enfleda and her court followed the Latin Rite.

Missionary work among the Angles and East Saxons
Fionán carried missionary work south of the Humber, baptising King Peada of the Middle Angles and sent Cedd and other monks as missionaries to Mercia and the kingdom of the East Saxons.

Tensions between Celtic and Roman ritual expression
In his time the tensions between Celtic and Roman ritual expression begin to emerge. In response to pressure from the queen and her advisers, Fionán agreed to allow Wilfrid, who was one of his monks, to go to Rome and explore contacts with the papacy. These tensions broke out more forcefully after his death.

Fionán struggled for ten years, supporting his missionaries in their work in the Midlands and East Anglia, and finding his rule at Lindisfarne increasingly threatened. He died before the Synod of Whitby was convened. Possibly the Roman party waited until after his death before embarking on the final confrontation, for he was a doughty opponent.