He came to the throne in 1005, after killing Kenneth III in battle. A year later he fought the English at Durham, was defeated, but retained the kingdom and, in 1018, while the English were preoccupied with Danish raiders, he marched south, won the battle of Carham, and secured Scotland's rights to Lothian.
He was later "invaded" by Canute the Great, who, it appears, may have taken Malcolm's homage, but left his kingdom otherwise unaffected, and have ratified the transfer of Lothian to Scots hands.
The battle of Carham does, however, appear to have been the seed that established the River Tweed as the traditional Anglo-Scottish border.
He married his daughter to the Norse Earl of Orkney, Sigurd the Stout, and allied himself with Owen the Bald, king of Strathclyde, but his attempt to annexe Strathclyde after Owen's death led to dissent and to Malcolm's death in 1034 at Glamis.
His other daughter, Bethoc, had married Crinan, the lay Abbot of Dunkeld, and their son, Duncan succeeded to the throne, as first king of the House of Atholl.
There are indications, given that other men, contemporary to Malcolm, are described as "king of Alba" (the older name for Scotland), that he may not have reigned over all of modern Scotland, but may have been restricted to a central band, between northern claimants and challengers, and the English (especially the earls of Northumbria) to the south.
Equally the claim that he married a daughter of the Irish king Brian Boru appears unsubstantiated. Another version has him marrying a daughter (Agatha) of Sigurd of Orkney, to whom Malcolm would later marry his own daughter. However, this appears impossible, since Agatha would have had to be born before her father.