Edward the Martyr was King of the English from 8 July 975 until he was killed in 978. He was the eldest son of King Edgar (r. 959-975). On Edgar's death, the succession to the throne was contested between Edward's supporters and those of his younger half-brother, the future King Æthelred the Unready. As they were both children, it is unlikely that they played an active role in the dispute, which was probably between rival family alliances. Edward's principal supporters were Dunstan, Archbishop of Canterbury, and Æthelwine, Ealdorman of East Anglia, while Æthelred was backed by his mother, Queen Ælfthryth and her friend Æthelwold, Bishop of Winchester. The dispute was quickly settled. Edward was chosen as king and Æthelred received the lands traditionally allocated to the king's eldest son in compensation.

Edgar had been a strong and overbearing king and a supporter of the monastic reform movement. He had forced the lay nobility and secular clergy to surrender land and sell it at low prices to the monasteries. Æthelwold had been the most active and ruthless in seizing land for his monasteries with Edgar's assistance. The nobles took advantage of Edgar's death to get their lands back, mainly by legal actions but sometimes by force. The leading magnates were split into two factions, the supporters of Ælfhere, Ealdorman of Mercia and Æthelwine, who both seized some monastic lands which they believed belonged to them, but also estates claimed by their rivals. The disputes never led to warfare.

Edward's short reign was brought to an end by his murder in March 978 in unclear circumstances. He was killed on the Dowager Queen Ælfthryth's estate at the Gap of Corfe in Dorset, and hurriedly buried at Wareham. A year later, his body was translated with great ceremony to Shaftesbury Abbey in Dorset. Contemporary writers do not name the murderer, but almost all narratives in the period after the Norman Conquest name Ælfthryth. Some modern historians agree, but others do not. Another theory is that the killers were thegns of Æthelred, probably acting without orders.

Medieval kings were believed to be sacrosanct, and Edward's murder deeply troubled contemporaries who regarded it as a mortal sin. He soon came to be revered as a saint, and his feast of 18 March is still listed in the festal calendar of the Book of Common Prayer of the Church of England. Edward was known in his own time for his extreme violence, and historians consider his veneration thoroughly undeserved. The historian Tom Watson comments: "For an obnoxious teenager who showed no evidence of sanctity or kingly attributes and who should have been barely a footnote, his cult has endured mightily well."