Called Malcolm the Maiden by later chroniclers, a name which may incorrectly suggest weakness or effeminacy to modern readers, he was noted for his religious zeal and interest in knighthood and warfare. For much of his reign he was in poor health and died unmarried at the age of twenty-four.
Earl Henry, who had perhaps been seriously ill in the 1140s, died unexpectedly at Newcastle or Roxburgh on 12 June, 1152, in the Northumbrian domain which David and he had done much to attach to the Scots crown in the decades of English weakness after the death of Henry I of England. Unlike the death of William Adelin in the White Ship, which had left Henry I without male heirs, Earl Henry had three sons. Thus, although his death damaged David's plans, and made disorders after his death very likely indeed, it was not a disaster.
As the eldest of Earl Henry's sons, although only eleven years old, Malcolm was sent by his grandfather on a circuit of the kingdom, accompanied by Donnchad, Mormaer of Fife, styled rector, perhaps indicating that he was to hold the regency for Malcolm on David's death. Donnchad and Malcolm were accompanied by a large army. As it turned out, Donnchad did not long survive David, holding the regency for a year before his death in 1154.
The Orkneyinga Saga claims "William the Noble", son of William fitz Duncan, was the man whom "every Scotsman wanted for his king". As William fitz Duncan married Alice de Rumilly in about 1137, young William can only have been a youth, perhaps a child. There is no sign that William made any claims to the throne. He died young, sometime in the early 1160s, leaving his sizable estates to his three sisters. Of William's other sons, Bishop Wimund had already been blinded, emasculated and imprisoned at Byland Abbey before David's death, but Domnall mac Uilleim, first of the Meic Uilleim, had considerable support in the former mormaerdom of Moray.
Another would-be king, imprisoned at Roxburgh since about 1130, was Máel Coluim mac Alaxandair, an illegitimate son of Alexander I. Máel Coluim's sons were free men in 1153. They could be expected to contest the succession, and did so.
As a new king, and especially as a young one, Malcolm could also expect challenges from his neighbours, with Somerled, King of Argyll, Fergus, Lord of Galloway and Henry II, King of England foremost among them. Only Rognvald Kali Kolsson, Earl of Orkney, was otherwise occupied, being on crusade, and his death in 1158 brought the young and ambitious Harald Maddadsson to sole power in the north.
The first opposition to Malcolm came in November of 1153, from the combination of a neighbour, Somerled of Argyll, and family rivals, the "sons of Malcolm", that is of Máel Coluim mac Alaxandair. This came to little as Somerled soon had more pressing concerns, firstly his war with Godred Olafson of Man which lasted until 1156 and secondly, perhaps, a conflict with Gille Críst, Mormaer of Menteith, over Cowal. Support for the sons of Máel Coluim mac Alaxandair may also have come from areas closer to the core of the kingdom, for two conspirators are named by chroniclers, one of whom died in trial by combat in February 1154.
In 1157, it is reported, King Malcolm was reconciled with Máel Coluim MacHeth, who was appointed to the Mormaerdom of Ross, which had probably been held by his father.
After a second meeting between Malcolm and Henry, at Carlisle in 1158, "they returned without having become good friends, and so that the king of Scots was not yet knighted. In 1159 Malcolm accompanied Henry to France, serving at the siege of Toulouse where he was, at last, knighted. "Whether this was the act of a king of Scots or of an earl of Huntingdon we are not told; it was certainly the act of a man desperate for knightly arms, but that did not make it any more acceptable in Scotland.
Malcolm returned from Toulouse in 1160. At Perth, Roger of Hoveden reports, he faced a rebellion by six earls, led by Ferchar, Mormaer of Strathearn, who besieged the king. Given that Earl Ferchar heads the list of those named, it is presumed that Donnchad II, Mormaer of Fife, was not among the rebels. John of Fordun's version in the Gesta Annalia appears to suggest a peaceful settlement to the affair, and both Fordun and Hoveden follow the report of the revolt and its ending by stating that the king led an expedition into Galloway where he eventually defeated Fergus, Lord of Galloway and took his son Uchtred as a hostage while Fergus became a monk at Holyrood, dying there in 1161. While it was assumed that the earls included Fergus among their number, and that the expedition to Galloway was related to the revolt, it is now thought that the earls sought to have Malcolm attack Galloway, perhaps as a result of raids by Fergus.
Some time before July 1163, when he did homage to Henry II, Malcolm was taken seriously ill at Doncaster. Scottish sources report that a revolt in Moray brought Malcolm north, and it is said that he
removed [the men of Moray] from the land of their birth, as of old Nebuchadnezzar, king of Babylon, had dealt with the Jews, and scattered them throughout the other districts of Scotland, both beyond the [Mounth] and this side thereof, so that not even one native of that land abode there.
Having made peace with Henry, replaced Fergus of Galloway with his sons, and resettled Moray, only one of Malcolm's foes remained, Somerled, by 1160 king of the Isles as well as of Argyll. In 1164, Somerled led a large army of Islesmen and Irishmen to attack Glasgow and Renfrew, where Walter Fitzalan had newly completed a castle. There Somerled and his son Gillebrigte were killed in battle with the levies of the area, led by the Bishop of Glasgow, probably Herbert of Selkirk at that time. The chronicles of the day attributed the victory to the intercession of Saint Kentigern.
Máel Coluim Cenn Mór, son of Henry, high king of Scotland, the best Christian that was of the Gaidhil [who dwell] by the sea on the east for almsdeeds, hospitality and piety, died.
Likewise, William of Newburgh praises Malcolm, "the most Christian king of the Scots", highly in his Historia Rerum Anglicarum.
Nonetheless, Malcolm was not well regarded in all quarters. The Gesta Annalia remarks
[Malcolm] quite neglected the care, as well as governance, of his kingdom. Wherefore he was so hated by all the common people that William, the elder of his brothers - who had always been on bad terms with the English, and their lasting foe, forasmuch as they had taken away his patrimony, the earldom of Northumbria, to wit - was by them appointed warden of the whole kingdom, against the king's will
According to legend, he had a daughter who was betrothed to Henry, Prince of Capua, on the latter's deathbed, but this is false as Malcolm had no heirs. His mother formulated a plan for a marriage to Constance, daughter of Conan III, Duke of Brittany, but Malcolm died before the wedding could be celebrated.
It is difficult, given the paucity of sources, to date many of the reforms of the Scoto-Norman era, but it appears that Malcolm continued the reforms begun by his grandfather and granduncles. The sheriffdoms of Crail, Dunfermline, Edinburgh, Forfar, Lanark and Linlithgow appear to date from Malcolm's reign, and the office of Justiciar of Lothian may also date from this period.
Malcolm founded a Cistercian monastery at Coupar Angus, and the royal taste for continental religious foundations extended to the magnates, as in Galloway, where the Premonstratensians were established at Soulseat by 1161.