Oswald Ernald Mosley (Sir Oswald on succeeding to the baronetcy as 6th Baronet in 1928) was born into a landed family of Rolleston, Staffordshire in 1896, his father being Sir Oswald Mosley, 5th Bart. After leaving Winchester School at the age of 16 he entered Sandhurst, and following the outbreak of the First World War was commissioned into the 16th Queen's Light Dragoons, but then applied to join the Royal Flying Corps and was posted to the Front. Back in England to take his pilot's certificate his leg was injured in a flying accident. He was recalled to his former regiment, but his damaged leg was affected by conditions in the trenches, and he was invalided out of the war in 1916.

An able though controversial figure and a powerful orator, long considered by both supporters and opponents as someone capable of holding high political office, Mosley's political career began in 1918 in a conventional way when he was selected as Unionist candidate for Harrow, and on election entered the National party coalition led by Lloyd George. His sympathy for the ordinary man who had fought so bravely in the trenches, concern for social objectives and dismay at governmental waste of money led him increasingly towards Liberal doctrines, and in November 1920 his condemnation in the House of Commons of Black and Tan atrocities in Ireland led to his crossing the floor to sit with the Liberals. His political career was to be strongly supported until her death in May 1933 by his wife Cynthia, daughter of Foreign Secretary Lord Curzon, whom he had married earlier that year and who became an M.P. in her own right. When in 1924 Ramsay MacDonald became the first Labour Party Prime Minister Mosley joined Labour as a member of the Independent Labour Party. At the subsequent election in Ladywood, Birmingham, he stood against the prominent Conservative Neville Chamberlain, being defeated by only 77 votes on a recount, and in 1926 he was selected as candidate for Smethwick, winning the subsequent election on a landslide. As unemployment rose steeply at the end of the decade, increased massively by the Depression which followed the Wall Street stock-market crash of 1929, Mosley, as Unemployment Minister, issued his Mosley Memorandum, which argued for the combatting of unemployment by spending money on public works, and on its rejection by the Cabinet resigned from the Government. In 1931 Mosley, supported by Labour dissidents, and with the use of £50,000 donated by Lord Nuffield, formed the New Party as an attempt to address the failings of the old political parties. The first by-election in May 1931 produced a creditable vote, but by splitting the non-Tory vote the New Party attracted Labour hostility when the Conservatives took the seat. Following consequent trouble at his meetings Mosley began to develop the use of stewards, and confrontations at meetings led to a loss of electoral support, and in 1932 the New Party was closed down.

Mosley was increasingly drawn to the perceived success of Italian Fascism in solving the serious social and economic problems of the time, in contrast to the seeming lack of purpose of the democratic multi-party system, visiting Rome and meeting Mussolini. In October 1932 the British Union of Fascists was formally launched, a party organised on military lines intended to reflect both the discipline and comradeship of the Armed forces experienced by Mosley in the Great War. The new movement met with initial success and by 1934 had attracted some 40,000 members, in addition to many thousands well disposed to it. But a large meeting at Olympia on the 7th of June 1934 met with concerted disruption, and the ensuing violence caused a significant reaction against the B.U.F. Organised opposition came initially mainly from Communists, bitter rivals of Fascism in the struggle to create a new world political order, and from Jewish groups determined to prevent Britain following German Nazism's strongly anti-semitic path. Increasingly, opposition attracted others who feared the threat to democratic freedoms posed by Fascism. The obvious visual parallels with the oppressive Nazi régime (blackshirt uniform, parades, the fascist salute, etc.) led to growing hostility and attempts to disrupt meetings. Although the party developed strengths in certain areas up to 1936 - the textile areas of Lancashire and Yorkshire, rural areas suffering from agricultural depression, and the East End of London where anti-semitism often underlay support - it failed to develop ultimately as a serious political force on the national scale.

The extent of Mosley's personal responsibility for deliberately encouraging anti-semitism, which existed as a background feature in areas of British society at that time, and with which British Union became associated as a movement, is a matter of continuing controversy. Disorder continued to characterise some of the meetings, though often they passed off peacefully, and organised hostility on the streets culminated in the "Battle of Cable Street" in London on October 4th 1936 when the police were unable to clear a way through a large crowd of anti-fascist demonstrators for a planned march through the East End. At this time Mosley married Lady Diana Mosley (the divorced Diana Guinness and one of the Mitford sisters) in Berlin, where Hitler attended the luncheon given by Frau Goebbels. At the end of that year the Public Order Act banned the wearing in public of uniform by members of political movements, and in March 1937 the party was plunged into a financial crisis during which many Headquarters staff, including William Joyce and John Beckett, were dismissed. The ominous growth of German military power and the growing likelihood of war fuelled hostility towards the British Union, which campaigned to keep Britain out of a European war, yet a Peace Rally which it held at Earls Court in July 1939 attracted an estimated 20,000 supporters.

Though war with Germany broke out in September 1939 the British Union, in common with pacifist and left-wing groups, was able to continue its campaign against the war policy as before. However, following the fall of France and the invasion crisis of May 1940 Defence Regulations 18B and then 18B (1A) were passed through Parliament by the Government, resulting in many leading British Union members, including Mosley and his wife, being arrested and interned without charge or trial on the grounds that they might potentially act as a Fifth Column of the enemy, an event regarded by those concerned as a slur on their often-expressed loyalty to the British state and crown. This episode, though it had in the dangerous circumstances of the time widespread public support, was one of major civil rights significance as it involved the imprisonment of individuals who had broken no law, and, as Churchill came to recognise, could be justified only in the most extreme circumstances. As the danger of invasion receded detainees were gradually released, and in November 1943 Mosley also was released from prison and placed under house arrest.

From 1945 to 1947 Mosley passed his time in farming in Wiltshire, but in February 1948, following the publication of his book The Alternative, he relaunched his political career as leader of the new Union Movement, campaigning on the slogan "Europe a Nation". The future would lie in cooperation between European peoples, coming together in a European nation-state, whilst colonies in Africa would be exploited to provide the food and other resources which Europe lacked. This policy contrasted with the programme of decolonisation which the post-war Labour Government was determined to promote. In his post-war movement Mosley renounced publicly both Nationalism and Anti-Semitism, whilst still predicting the collapse of Capitalism and the coming fight against Communism. The new party was much less militaristic in organisation than its predecessor, and repudiated the term "fascist" as a description of its political identity. However, the climate of deep hostility to Fascism which the war, widely regarded in Britain as a crusade to preserve democratic freedoms and humane values, had engendered, ensured that the new movement never achieved the level of success of its predecessor. As immigration from the West Indies began to rise substantially Mosley declared the Union Movement against such immigration, and though this policy gained some temporary support further controversy and hostility developed. In 1953 he founded The European journal (which lasted until 1959), and in 1954 urged withdrawal from the Middle East, foreshadowing the Suez Crisis of 1956. But the predicted economic collapse, which in the exhaustion and severe shortages of the post-war period had seemed a likely development, and which would have afforded a political opportunity to a strongly-led movement, failed to happen, and despite its populist advocacy of repatriation for West Indian immigrants in 1959 the party failed to gain any significant electoral support amongst a nation which the horrors of World War II, awareness of the Holocaust and other Nazi atrocities, a potentially disastrous Cold War, and growing economic prosperity all rendered deeply suspicious of extremist policies of any political colour. As the Union Movement declined other divergent but essentially minor fascist-style groups began to emerge. In 1966, at the age of 70, Mosley resigned his leadership of Union Movement. In October 1968, after publication of his controversial autobiography My Life, his "Panorama" television interview attracted a record 8.5 million viewers, a testimony to the public's continuing interest in his political career. Sir Oswald Mosley died in December 1980.