Alexander George Robertson Mackenzie was an architect, the second son of architect Alexander Marshall Mackenzie (1848-1933), under whom he trained from 1894 to 1898.
Father and son were in practice together from 1902 to 1933, with offices in Aberdeen and London. They designed the Waldorf Astoria Hotel and Australia House, both in Aldwych. They also worked on the conservation of historic buildings, including restorations of churches and castles in Aberdeenshire.