Who became the first female Prime Minister of the United Kingdom?

Margaret Thatcher entered Downing Street in 1979 after leading the Conservative Party to victory, and stayed until 1990, the longest continuous run in the office in the twentieth century. She had become party leader in 1975 by challenging a sitting former prime minister when better-placed rivals hesitated, which says something about how the opportunity arose. Her governments pursued a programme of privatising state-owned industries, curbing the legal powers of trade unions, controlling inflation through monetary policy and cutting direct taxation, changes that were contested at the time and remain politically divisive. The Falklands conflict of 1982 and the year-long miners' strike defined her middle years in office. She was eventually removed not by an election but by her own party, after a leadership challenge triggered by cabinet resignations and the unpopularity of a new local tax. The United Kingdom has had further female prime ministers since.

The office of prime minister is not defined by any single statute; it grew by convention over centuries.