[1] The fourth and youngest son of Andrew Fisher McCallum, a master dyer, and his wife, Catherine Buchanan Gibson, he was educated at Paisley Grammar School and Trinity College, Glenalmond.
Returning to Britain, he obtained a place at Worcester College, Oxford, where he read history and took his degree with first class honours in 1922.
[4] McCallum defended David Lloyd George against those who had attacked him for his conduct during the 1918 election and for his policies at the Paris Peace Conference.
[5] Max Beloff called Public Opinion and the Last Peace "scholarly and penetrating", adding that it was "one of the most important, as it is certainly one of the most brilliant and courageous, contributions to the literature of the subject".
In 1967, he resigned the mastership of Pembroke to become principal of what, the following year, was named the King George VI and Queen Elizabeth Foundation of St Catharines housed at Cumberland Lodge, Windsor Great Park.
The professor coined the word psephology to describe the academic study of elections, but in this retained his focus as a historian and did not venture into sociological approaches.