John Harold Clapham was the son of a Wesleyan Jeweler in Salford, Lancashire. He attended King's College, Cambridge, on a scholarship, graduating with first-class honors in history in 1895. He received the Lightfoot scholarship in ecclesiastical history the following year and the Prince Consort Prize in 1897 and then was made a fellow of King’s. He was influenced most in these early years by the economist Alfred Marshall.
In 1902 Clapham went to the University of Leeds as a professor of economics and a pioneer in economic history. He returned to Cambridge in 1908 as dean of King's and was deeply involved in university affairs until his death. In 1928 the Cambridge chair in economic history was established for him, and he held it for a decade.
Clapham was a member of the Board of Trade on the Cabinet Committee on Priorities (1916-1918), president of the British Academy (1940-1945), editor of Studies in Economic History, and joint editor of the first volume of the epochal Cambridge Economic History of Europe (1941). He was knighted in 1944.
In 1945 Clement Atlee appointed Clapham chairman of a committee to study economic and social research in England. The committee's recommendations, published after Clapham's death, were accepted and implemented by the government.
Clapham was essentially uninterested in the role of ideas, and in 1922 his famous essay "Of Empty Boxes" attacked theory and analysis which "outran verification." During the 1930s and 1940s, when disagreements on methodology and meaning stirred historians and social scientists, he continued to support narrative histories of institutions based on accumulations of economic data. In his monumental three-volume Economic History of Modern Britain (1926-1938), Clapham traced with admiration the achievements of 19th-century free enterprise. Personally sympathetic to the economically displaced, Clapham wrote little about them and even less about the causes for their displacement.