The son of an Irish labourer, Clynes went to work in a cotton mill at the age of 10. From 1889 he was a trade-union officer, and, during his parliamentary career (1906–31, 1935–45), he was president of the National Union of General and Municipal Workers (1912–37). He served as minister of food briefly in 1918.

In 1919 Clynes served as deputy leader of the Labour Party in Parliament, and he then became leader (1921–22) until he was defeated by Ramsay MacDonald and thereafter was deputy again. When MacDonald formed his coalition National Government in August 1931, Clynes joined most of his fellow Cabinet members in opposition and was defeated for reelection to Parliament in October of that year. Although eventually returned to the House of Commons, he was never again in a Cabinet office. His two-volume Memoirs appeared in 1937.