English politician who was the leader of the British Union of Fascists from 1932 to 1940 and of its successor, the Union Movement, from 1948 until his death. These groups were known for distributing anti-Semitic propaganda, conducting hostile demonstrations in the Jewish sections of east London, and wearing Nazi-style uniforms and insignia.

Serving in the House of Commons from 1918 to 1931, Mosley was successively a Conservative, an Independent, and a Labour Party member, serving in a Labour ministry in 1929–30. In 1931 he tried to form a socialist party but was defeated for reelection to Parliament. The next year he founded the British Union of Fascists, for which some enthusiasm was generated by his own powerful oratory and by the support of the newspaper publisher Viscount Rothermere. Interned after the outbreak of World War II, Mosley was released in 1943 because of illness. On Feb. 7, 1948, he launched the Union Movement, which he described as an amalgam of 51 organizations, most of them right-wing book clubs.

Mosley married in 1920 Lady Cynthia Blanche Curzon (died 1933), daughter of the 1st Marquess Curzon of Kedleston; and in 1936 Diana Guinness (née Freeman-Mitford), daughter of the 2nd Baron Redesdale, himself a prewar apologist of Nazi Germany. Mosley's autobiography, My Life, was published in 1968.