Refuge in Iona
Oswald was the son of Ethilfrith, king of Berenicia who united Deira to form the kingdom. But when Edwin seized that kingdom in 616, Oswald and his brothers fled to Scotland. They found refuge in Iona where Oswald became a Christian. On Edwin's death in 633, Oswald returned and whereas his two brothers were killed by the British king, Cadwalla, Oswald defeated him a year later at Heavenfield near Hexham.

Brings Aidan to Lindisfarne
Oswald attributed his victory in this battle to the fact that before the battle he had set up a cross and prayed to Jesus. So now that he was victorious, he sent to Iona for monks to come and preach Christianity in Northumbria. The first monk to come was Colmán. but he was quite severe and thought all Northumbrians were barbarous and only antagonised his listeners. He was withdrawn and replaced by Aidan, whose more gentle preaching Oswald translated and to whom Oswald gave the island of Lindisfarne, near his palace at Bamburgh, as his monastery and episcopal see.

Expansion and death
Oswald united Bernicia and Deira into his one kingdom of Northumbria. He married Cyneburga, daughter of Cynegils, king of Wessex, whose baptism Oswald sponsored. Perhaps because his expansionist policies, Oswald ran into opposition and after only eight years at the age of 38 he was killed by Penda, king of Mercia, at the battle of Maserfield (identified as Oswestry in Shropshire). Bede says that as he fell, he was heard to pray for the souls of those who died with him. Oswald's body was mutilated in  sacrifice to Woden, but his members were recovered. It was said his head was brought to Durham, but there are claims that there are four claimed heads of Oswald on continental Europe.

Memorial church at Heavenfield
A Church of Saint Oswald stands on the location of the wooden cross left by Oswald at Heavenfield, the night before the battle. It is visible from the B6318 Military Road that runs alongside the Roman Wall.