He came from a West Riding clothier and Manchester manufacturing WM background and was educated at The Leys School and Cambridge University. He was for a time a local preacher, but later worshipped with Anglicans. In 1907 he was appointed Professor of Economics at Yorkshire College, Leeds, moving to Cambridge the following year, becoming Professor of Economic History in 1928 and Vice-Provost of King's College in 1933. His major work, known to historians as 'Clapham', is the 3-volume Economic History of Modern Britain (1926-1938). His son, Sir Michael John Sinclair Clapham KBE (1912-2002), classicist, printer and discoverer of how to enrich uranium, became a director of ICI and was President of the CBI 1972-1974. He died on 11 November 2002. A daughter, Margaret Alison Clapham (1908-1993) married the Ven. Weston H. Stewart (d.1969), Archdeacon in Palestine, Syria and Transjordan.