The son of Albert Ehrman, John was educated at Charterhouse School and Trinity College, Cambridge, when the outbreak of war in 1939 interrupted his studies.
He returned to Trinity College after the war and his work gained him the admiration of G. M. Trevelyan and George Clark.
Roy Jenkins estimated that it took Ehrman about 40 years to complete but that it was "thoroughness rather than the flickers of alternative temptation which made him slow".
It is hardly a biography, and indeed it is not clear that Pitt had an inner life to biographize, but it is a consummate account of the political 'life and times'.
The author's determination to deal with every episode in detail sometimes blurs the perspective, but readers can be assured that each topic has been thoroughly researched and that Ehrman's analysis is invariably judicious".