He was son of Malcolm III (Máel Coluim mac Donnchada) and his first wife Ingibiorg Finnsdottir, widow of Thorfinn Sigurdsson, earl of Orkney.

Edgar Ætheling, the last remaining male member of the English royal family, had fled to Scotland in 1068, seeking protection from the invading Normans.

In 1070, possibly claiming he was redressing the wrongs against his brother-in-law, Malcolm responded with a "savage raid" of Northern England.

[8] While marching north again, Malcolm was ambushed by Robert de Mowbray, Earl of Northumbria, whose lands he had devastated, near Alnwick on 13 November 1093.

[9] The resulting power vacuum allowed Donald III of Scotland (Domnall Bán mac Donnchada), younger brother of Malcolm, to seize the throne.

The new monarch represented the interests of "a resentful native aristocracy", driving out the Anglo-Saxons and Normans who had come to the court of Malcolm and Margaret.

Donald III had been unable to gain the support of certain landowners and church officials of the Scottish Lowlands, who had ties to the regime of his predecessor.

The Lowlands rebels seem to have ceased their activities, but Donald had spent the intervening months rebuilding his army and political support.

The Annals of Ulster report that "Donnchad son of Mael Coluim, king of Scotland, was treacherously killed by his own brothers Domnall and Edmond".

In Chronicle of the Picts and Scots (1867), there is a 13th century entry recording that Duncan was killed by Máel Petair (Malpeder), through the treachery of Donald.

John of Fordun (14th century) finally recorded the better known account of the event, that Duncan was "slain at Monthechin by the Earl of Mernys ... through the wiles of his uncle Donald".

His supporters would have had reason to feel threatened by the large number of Anglo-Saxons who had arrived in Scotland under the reign of Malcolm III.

Magnus III of Norway and his fleet were campaigning at the Irish Sea, attempting to establish his authority over the Kingdom of the Isles.

Duncan himself was obviously supported by William II of England, who lent him "a numerous army of English and Normans".

His half-brother Edgar, King of Scotland, only managed to gain the throne due to the intervention of William II, his claims again opposed by most of the Gaels.

The effects of Edgar's victory were significant, as Anglo-Saxon laws, institutions, and forms of government were adopted in the Kingdom of Scotland.

Hudson feels that Duncan II doomed his own reign by the "fatal move" of sending away his foreign troops, thus divesting himself of his own supporters.

He feels that the male-line descendants of Malcolm III and Saint Margaret managed to hold onto the throne until the 13th century precisely because none of them made the same mistake.

He points out that Edgar succeeded in holding the throne for a decade because he continued to depend on aid from his political patrons, William II and Henry I of England, who had resources far surpassing those of Donald III and his supporters.

The last remaining Meic Uilleim, an infant daughter of Gille Escoib or one of his sons, was put to death in 1229 or 1230: "[T]he same Mac-William's daughter, who had not long left her mother's womb, innocent as she was, was put to death, in the burgh of Forfar, in view of the market place, after a proclamation by the public crier.

[17] The sole surviving charter of Duncan II granted Tynninghame and its surrounding area to the monks of Durham.

He was closely associated with the royal household for decades, his own descendants forming the landowning dynasties variously known as Uviet(h)s, Eviot(h)s, and Ovioths, with certain lines enduring to the 17th century.

[18] The history of George Buchanan considers Duncan to have been summoned to Scotland by its people, as Donald had alienated "all good men who had a veneration for the memory of Malcolm and Margaret" and those nobles refusing to swear allegiance to him.