Edwin was a prince of the royal house of Deira. In 604 he had to flee from his home when Æthelfrith, king of the neighbouring Bernicia, invaded Deira and took over the state and assumed the throne. It was Æthelbert's intention to merge the two states and their ruling houses and to this end he married Edwin's sister Acha.
As an exile, Edwin took refuge in Mercia, the English midlands, with its king Cearl and entered into an alliance through a marriage with his daughter Cwenburh. Their sons Osfrith and Eadfrith were born during this period of exile. So long as Edwin was alive he represented a threat to Æthelfrith who turned his attention southwards and won a military victory near Chester. This drove Edwin went further away, to the court of King Rædwald of East Anglia who was the most powerful English king of the day. Here too he was pursued by Æthelfrith's agents who tried on several occasions to bribe Rædwald to have him killed. Rædwald refused and in 616 he raised an army against Æthelfrith whom he defeated and killed in battle beside the River Idle, just south of the Humber. Æthelfrith's sons Oswald and Oswiu fled northwards and Edwin was installed as king, beginning his reign subject to Rædwald's overlordship.
Rædwald's death in 624 or 625 gave Edwin room to act in his own right. More than that, it meant he and the other kings who had been subject to Rædawld's influence had to begin re-negotiating the diplomatic and military alliances on which they depended. Edwin turned to Kent and an alliance with King Eadbald which he consolidated with a marriage to the Kentish king's sister Æthelburh. Looking to the south in this way, he may have been attempting to counterbalance potential dangers from the Britons and the Scots to the north where Æthelfrith's sons were at large, a challenge to him as he had been to their father.
The alliance with Kent intoduced Christianity into Northumbria for the first time, for Æthelburh was a Christian princess. According to the terms of the marriage agreement, she was to be free to practise her religion and to have her own priest in her household. This was Paulinus, an Italian priest who was at the time part of the Canterbury mission. Edwin himself, however, did not immediately take up Christianity. The catalyst to his conversion came on Easter Sunday of 626 when he survived an attempt on his life at the hands of an assassin sent by the West Saxon king Cuichelm. An immediate effect of the shock of this crisis was to send the pregnant queen into labour and their daughter Eanflaed was born during the following night.
Edwin was bound to respond to the provocation from the West Saxons and, according to Bede's account, he promised to accept the Christian faith if he were granted victory. He mounted a campaign, leading his army right into the south of England, where he was indeed victorious. This immediately transformed Edwin's standing. From being a leader with little military reputation, he became acknowledged the most powerful English king of his day. Bede lists him as one of the seven kings who at different times were overlords of others. He commanded authority over all the English kings, except in Kent, and he ruled also over the Britons, even bringing the islands of Anglesey and Man under English rule. Within his own Northumbrian realm, Edwin's position was strengthened, for the wealth which began to flow into the kingdom as tribute from elsewhere increased Edwin's capacity to give largess and patronage to his own supporters.
This, then, is the context whithin which Edwin formally accepted Christianity. He was able to represent the Christian God as one who brings success and, both through the religious practices and the overlordship of the southern kingdoms, Edwin was able to define a style of kingship as distinctively his own, contrasting with that of Æthelfrith and the Bernicians who preceeded him.
Yet, even at the height of his power, Edwin could not impose the new religion on his followers except by their consent. Bede gives a vivid account of a debate held in the king's council in the winter of 626-7 at which Paulinus made his case. One of councillors then said that human life as we understand it is like a sparrow which flies into the warmth and light of the feasting hall from the darkness and storms outside, and then flies out again into darkness through the opposite door. We see the life on earth, but of what goes before or after we have no knowledge. Paulinus has now spoken of this: let us accept his teachings. The chief priest of the old religion, Coifi, led the way by desecrating and destroying his shrines. Edwin and his court were then baptised the following Easter, after which Paulinus preached more widely in the kingdom and carried out mass baptisms.
Through his acceptance of Christianity, Edwin gained within his administration a clergy who had skills of literacy which were previously unknown in the kingdom and who depended for their position on him without reference to any traditional tribal or factional loyalties. They could record in writing the tributes due to the king from subject people and could enable Edwin to enter into correspondence with the Pope in Rome. Bede saw a Roman dimension to Edwin's kingship, in the way in which he appeared about the kingdom preceded by a standard-bearer and with Roman-type banners paraded before him. He enforced law and order so that, according to the saying, a woman with a new-born child could walk from coast to coast without coming to harm. He had bronze drinking cups provided at roadside springs and, out of both fear and love for the king, nobody vandalised them.
In the end, the challenge to Edwin came not from Æthelfrith's sons in the north, but from an alliance of the Mercian king Penda and the Welsh king Cadwallon, both of whom are likely to have suffered as a result of Edwin's growing power to the south. They raised an army against Edwin and killed him in battle in 633 in the fenlands at Hatfield, near to Doncaster. Æthelburh fled back to Kent with her children as the kingdom was ravaged by the invaders.
