Details of her life and identity come from Bede's Historia Ecclesiastica, the Anglian collection and the Lives of Edwin of Northumbria and Hilda of Whitby.
Multiple envoys from Æthelfrith offered bribes and then threats to try to persuade Rædwald to murder his guest or turn him over to them.
Rædwald was inclined to do so until admonished by his pagan queen for acting in a manner dishonourable for a king by betraying a trust for fear or greed.
Edwin and his household, including Breguswith and her daughters Hereswith and Hild, were baptised by Paulinus at York in the spring of 627.
This royal alliance suggests that Æthilric was expected to rule and was either already Christian, or had accepted the faith in consequence of the marriage.
The identity of Hereswith's husband Æthilric is shown in the East Anglian dynastic tally known as the Anglian collection and in the list given in the Historia Brittonum, since Æthilric is in both cases shown as the father of Ealdwulf and Bede states that Hild was Ealdwulf's aunt.
It is unlikely that other versions which make her the wife of Æthelhere or of Anna can be correct, since her departure for the religious life in Gaul preceded their deaths.
The Anglian collection also lists Ælfwald of East Anglia as the son of Ealdwulf, and not of Athilric and Hereswith, as is sometimes stated.
After staying for one year in East Anglia in 647, Hild returned to Northumbria to rule the monastery of Hartlepool and later founded the royal Northumbrian abbey and mausoleum of Whitby, where Edwin was enshrined.