Born in Edinburgh, Mackie was educated at Middlesbrough High School and Jesus College, Oxford, where he took a first-class degree in history and won the Lothian Essay Prize.
[1] During the First World War, he served in the Argyll and Sutherland Highlanders and was awarded a Military Cross.
However, he never regained full use of his left hand and suffered considerable pain for the remainder of his life.
He returned to St Andrews after the war, before being appointed professor of modern history at Bedford College, University of London, in 1926.
Mackie returned to the University of Glasgow lecture hall in 1961 in the capacity of emeritus professor.