Haedda was born in Yorkshire, supposedly at Headingley, near Leeds, which takes his name.

He was educated at Whitby Abbey and became a monk there and, afterwards - so tradition says - at Glastonbury Abbey in Somerset. He must have attracted the attention of the ecclesiastical hierarchy there, for, in AD 676, Archbishop Theodore appointed him Bishop of Wessex.

Haedda was a holy and virtuous man, as well as a clear-headed statesman. In AD 688, he persuaded King Caedwalla of Wessex to resign his throne in order to go on a pilgrimage to Rome and, later, assisted King Ine in framing his code of good and wholesome laws. Haedda is best known, however, for, around AD 690, removing the seat of the Bishopric, from its original foundation at Dorchester-on-Thames, to Winchester, where the new cathedral adjoined the Royal palace. Along with his administration, apparently went the body of St. Birinus, founder of the see. Though this was hotly disputed in later centuries.

Haedda apparently kept up his associations with Glastonbury. His name was recorded on one of the famous 'pyramids' or cross-shafts which marked the supposed grave of King Arthur in the old cemetery there. It has been suggested that it commemorated a visit during which Haedda attempted to irradicate the last remnants of Celticization in the Western Church. Haedda ordained St. Guthlac, but his only known foundation is the Church of Farnham in Surrey. He died at Winchester on 7th July AD 705.