Œthelwald had become king of Deira in 651 after Oswine of Deira was killed by Oswiu of Bernicia; it is uncertain whether Oswiu (who was Œthelwald's uncle) installed him as king or whether Œthelwald took the kingship in opposition to Oswiu.

Œthelwald, a pious Christian, rejects Oswiu's overlordship and turns instead to the pagan Penda, who mounts another attack on Bernicia.

Talorgan I, nephew of Oswiu, is crowned king of the Picts.

He probably accepts Northumbrian overlordship and pays tribute.

He is the son of Eanfrith of Bernicia, who had fled into exile among the Picts after his father, Æthelfrith of Northumbria, was killed around the year 616.

Eanfrith had married a Pictish princess, and their son is Talorgan.

Œthelwald in 655 assists Penda during his invasion of Northumbria.

However, when the armies of Oswiu and Penda meet at Cock Beck, near what later will be Leeds, on November 15 at the Battle of the Winwaed, Œthelwald withdraws his forces, as does Cadafael Cadomedd of Gwynedd.

Penda is defeated and killed, perhaps in part because of this desertion, and afterward Œthelwald seems to have lost Deira to Alchfrith, who is installed there by the victorious Oswiu.

Œthelwald's fate is unknown, as nothing is formally recorded of him after the battle.

Local tradition, however, held that he became a hermit in Kirkdale, North Yorkshire.

The battle has a substantial effect on the relative positions of Northumbria and Mercia.

Mercia's position of dominance, established after the battle of Maserfield, is destroyed, and Northumbrian dominance is restored; …

Mercia itself is divided, with the northern part being taken by Oswiu outright and the southern part going to Penda's Christian son Peada, who has married into the Bernician royal line (although Peada will survive only until his murder in 656).

Northumbrian authority over Mercia will be overthrown within a few years, however.

Significantly, the battle of the Winwead marks the effective demise of Anglo-Saxon paganism.

Penda had continued in his traditional paganism despite the widespread conversions of Anglo-Saxon monarchs to Christianity, and a number of Christian kings had suffered death in defeat against him; after Penda's death, Mercia is converted, and all the kings who rule hereafter (including Penda's sons Peada, Wulfhere and Æthelred) are Christian.

Oswiu, now become overlord (bretwalda) over much of Great Britain, establishes himself as king of Mercia, setting up his son-in-law, Penda's son Peada, as a subject king over Middle Anglia.

Peada founds Peterborough Cathedral, which becomes one of the first centers of Christianity in England.

Deusdedit is consecrated as the archbishop of Canterbury.

Œthelwald of Deira, because of his desertion at the Battle of the Winwaed, is removed from office by his uncle Oswiu and replaced by the latter's son Alhfrith, as subject king in a united Northumbria.