William Mackay Mackenzie (1871–1952) was a Scottish historian, archaeologist and writer, who was Secretary of the Royal Commission on Ancient and Historical Monuments of Scotland between 1913 and 1935, and also an expert on folk-lore. He was born in Cromarty, graduated MA at Edinburgh University and taught at Glasgow Academy between 1896 and 1912. He also had a DLitt.
In 1925-1926 he was Rhind lecturer in Archaeology at Edinburgh University and during the Second World War acted as head of the department of Ancient Scottish History. In 1942 he was appointed to be a member of the Commission where he had formerly been Secretary. He was a Fellow of the Society of Antiquaries of London (FSA) and was made an honorary Doctor of Laws in 1949 at Edinburgh. As well as writing on medieval history, he published a major edition of Dunbar's poems. His younger brother, Donald Alexander Mackenzie, was also a prolific writer on religion, mythology and anthropology.