He was the son of the West Saxon king Edward the Elder (Edward) (reigned 899–924) and Eadgifu and the half brother of King Athelstan (reigned 924–939), under whom the political unification of England had been accomplished. On Athelstan's death (939), Olaf Guthfrithson, the Norse king of Dublin, occupied Northumbria and raided the Midlands.

Edmund recovered the Midlands after Olaf died in 942, and in 944 he regained Northumbria, driving out the Norse kings Olaf Sihtricson and Raegnald. He captured Strathclyde in 945 and entrusted it to Malcolm I, king of Scots, in return for a promise of military support. Thus, Edmund inaugurated a policy of establishing a secure frontier and peaceful relations with Scotland and through his laws sought to curtail feuds. In addition, his reign marks the beginning of the 10th-century monastic revival in England. The king was killed in his palace by an exiled robber and was succeeded by his brother, Eadred (reigned 946–955); Edmund's sons eventually acceded to power as kings Eadwig (reigned 957–959) and Edgar (reigned 959–975).