Clan Morrison is a Scottish clan. The Highland Clan Morrison is traditionally associated with the Isle of Lewis and Harris (Leòdhas) around Ness (Nis), Dun Pabbay, and Barvas (Barabhas), lands in Sutherland around Durness, and in North Uist. There are numerous Scottish clans, both Highland and Lowland, which use the surname Morison or Morrison. In 1965, the Lord Lyon King of Arms decided to recognise one man as chief of all Morrisons, whether their clans were related or not.

The Morrison clan centred on the Isle of Lewis derived their surname from MacGilleMhoire, a name said to mean "son of a servant of Mary". ("Mhic" meaning son, "Gille" meaning servant and "Mhoire" meaning Mary). In time this Gaelic surname was Anglicised as Morrison. The chiefs of the clan were the Morrisons of Habost and Barvas, and held the hereditary office of brieve. On consequence of this position the clan was also known as Clann-na Breitheamh. The Morisons held this office until 1613; and by the 19th century it was considered impossible to trace their descendants. The original spelling of the name is "Morison" with one "r", but in the early 19th century the spelling "Morrison" became popular. There are also alternative spellings, or septs, such as Gilmore. They were a numerous clan in Lewis, the population in 1861 numbered 1402, or one fifteenth of the population. These numbers indicate a domination of the island for many centuries.

Besides areas around the north of the Isle of Lewis, many Morrisons traditionally live in the north-west Highlands, in the county of Sutherland around Durness (Scottish Gaelic: Diùranais), together with their traditional allies, the Clan Mackay. "Many sanguinary battles, still recounted by tradition, were fought between the Mcleods and Macaulays on one side and the Morisons on the other. At last the Morisons were forced to leave Lewis and take refuge with that part of their clan which was settled in Duirness and Edderachyllius, Sutherland, where still, in 1793, the natives were all, except a few, of the three names of Mac Leay, Morison or Mcleod."

A group of the bardic Ó Muirgheasáin clan settled on the isle of Harris around 1600 under the service of the MacLeods of Harris and Dunvegan. At around this time, the file Ó Muirgheasáin replaced the bard Mac Gille Riabhaich, to the MacLeods of Harris and Dunvegan. The Ó Muirgheasáins ultimately had roots in the north of Ireland, within "O'Neill's country". The clan is thought to have established itself in the Inner Hebrides, on the isle of Mull, by 1512, likely patronised by the MacLeans of Duart. Despite their long service to the MacLeans and MacLeods, not one Ó Muirgheasáin poem, written for the MacLeans of Duart, exists to this day, and the earliest piece of poetry written for the MacLeods of Harris and Dunvegan only dates to 1626. In time the Harris Ó Muirgheasáins Anglicised their surname to Morrison. The Irish Gaelic Ó Muirgheasa means "descendant of Muirgheas". The personal name Muirgheas may be derived from the Gaelic elements muir, meaning "sea", and geas, meaning "taboo", "prohibition".

The surname Morrison is derived from the patronymic form of the personal name Morris. This personal name is a variant of Maurice, and was quite popular in the Middle Ages. The mainland Morrisons descend from a Norman named Maurice. The senior line of the mainland Morrisons were the Morisons of Bognie in Aberdeenshire. Many of the mainland and lowland Morrisons derived their name this way. The Morrisons of Perth and Lennox derive their surname in this way.

Within the north-east of Scotland, the Morisons of Bognie, in Aberdeenshire, are the principal Morison family. They are thought to be unrelated to the west coast (and Hebridean) Morrisons. The British royal family can claim direct descent from the early Morisons of Bognie through the maternal line of Lady Diana Spencer, Princess of Wales. In the aftermath of the infamous Fire of Frendraught, Alexander Morison acquired the lands of Bognie from Sir James Crichton of Frendraught in 1635, becoming the 1st Baron of Bognie. His son George Morison, 2nd Baron of Bognie, married Christian Urquhart, Viscountess Frendraught (the widow of James Crichton, 2nd Viscount Frendraught). The current representative of the family is Alexander Gordon Morison, 14th Baron of Bognie and Mountblairy. His son, Conner Morison, holds the Arms of the Younger of Bognie and Mountblairy.

The coats of arms of the Morisons of Dersay (or Darcie), in Fife; and the Morisons of Bognie; and the Morisons of Prestongrange utilise Moor's heads. This is a pun on the surname; an example of canting arms. According to the 19th-century historian William C. Mackenzie, it is uncertain whether or not these Morisons have any connection with the Lewis Morisons. Mackenzie noted that in the beginning of the 17th century, a son of the laird of Darcie went to Lewis to negotiate for the release of the Fife adventurers who had been held hostage.

In the late 17th century, the origin of the clan was documented within an historical account of Lewis written by John Morrison of Bragar, 'Indweller' of Lewis. The Indweller wrote this account sometime between about 1678 and 1688 and stated that the early inhabitants of Lewis were three men from three separate races.