He was born in Birkenhead, the child of school-teachers and was educated at Birkenhead School and Oxford University. He taught at Oxford from 1971–1984 and was twice married. He helped to found the left-wing journal History Workshop Journal. Mason specialized in the social history of the Third Reich, especially that of the working-class. Mason's most famous books were his 1975 work Arbeiterklasse und Volksgemeinschaft (The Working Class and the National Community), a study of working-class life under the Nazis and his 1977 book, Sozialpolitik im Dritten Reich (Social Policy in the Third Reich). Unusually for a British historian, most of his books were originally published in German first.