The Deiran exile Hereric had been poisoned while at the court of Ceretic, king of Elmet; Æthelfrith may have been responsible for this killing.

Edwin, apparently seeking safety from Æthelfrith, seems to have traveled between many different kingdoms during his period of exile.

He may have spent time during his exile in the British kingdom of Gwynedd, and it seems clear that he spent time in Mercia, because he married a daughter of king Cearl.

Edwin ended up in East Anglia, under the protection of its king, Raedwald.

Æthelfrith had sent messengers to bribe Raedwald with "a great sum of money" into killing Edwin; Bede reports that his first message had no effect, but Æthelfrith had sent more messengers and threatened war if Raedwald did not comply (bribes and threats of this kind may have previously been used to accomplish Hereric's killing.)

Raedwald had eventually agreed to kill Edwin or hand him over to Æthelfrith's messengers, but was reportedly dissuaded from this by his wife, who said that such a thing was unworthy of his honor.

Instead, Raedwald raises an army and marches against Æthelfrith, and around 616 Æthelfrith is defeated and killed on the east side of the River Idle by an army under Raedwald; Bede says that Æthelfrith had the inferior army, because Raedwald had not given him time to bring all his forces together.

While presented by Bede as being fought simply over the issue of Edwin, this war may have actually involved questions of power and territory between the two rulers.

Æthelfrith's heir, prince Eanfrith, seeks refuge with his mother's family, probably in Gododdin (modern Scotland) and moves further north into Pictland.

Æthelfrith's younger sons Oswald and Oswiu escape to the court of king Eochaid Buide of Dál Riata, where they are soon converted to Christianity by the monks of Iona.