There are two clans of this name which have no family connection with each other. Firstly there are the MacAulays of Ardencaple, Dunbartonshire who are believed to be of Irish origin and claim to be descendants of the Siol Alpin. It has been suggested that they are descended from a son of Alwyn, Earl of Lennox.

Alexander de Ardincaple who lived during the reign of James V was the first to adopt the name MacAulay. In 1591 the chief of these MacAulays entered into a bond of manrent with Macgregor of Glenstrae which acknowledged the clan as a cadet branch of the Macgregors. Several generations later in 1694 the then chief again signed a bond of manrent, this time with Sir Duncan Campbell of Achinbreac where they again state they are Macgregors. In 1613 John Dow McAlwa and his son Awla McAlwa were fined for the reset of members of the Clan Gregor. The line ended with the 12th Chief Aulay MacAulay who in 1767 sold the lands of Ardencaple to the Duke of Argyll.

After this many of the clan settled in areas as far apart as Argyll, Sutherland and Caithness. The Hebridean MacAulays trace their descent from Aula or Olave "the black", last King of Man and the Isles who lived during the early 12th century.

The MacAulays held Luig on the Isle of Lewis where they were followers of Siol Torquil, the Macleods of Lewis and were bitter enemies of the Morrisons. Although little has been written of this clan the Lewis MacAulays appear to have faired better than their southern namesakes. Among their numbers were Lord MacAulay (1800-59) the famous essayist and historian, several notable clergymen and a general in the East India Company