He was son of Edgar (king) and Elfrida. He came to the throne on the death of his half brother. He had an interrupted reign, abdicating in favor of  Sweyn in 1013 and coming to the throne again after Sweyn's death just a year later. By his first marriage to Elgiva he might have had as many as 13 children, although there is uncertainty. By his second marriage to Emma, daughter of the Duke of Normandy, he had three children, one of whom, Edward the Confessor, ultimately succeeded him. He was known as the 'unraed' or 'unrede.' which means 'without counsel.'

His reign was interrupted by the usurpation of Sweyn, son of Harold Bluetooth, king of Denmark. Sweyn claimed the throne by right of conquest, but enjoyed its privileges for less than a year before he died and Ethelred was able to reclaim the throne.