The first female Prime Minister of the United Kingdom was Margaret Thatcher. She served as Prime Minister from 1979 to 1990, making her the longest-serving Prime Minister of the 20th century. Margaret Thatcher was a prominent figure in British politics and led the Conservative Party. Her tenure as Prime Minister was marked by significant political and economic reforms, including privatization, deregulation, and conservative policies. Thatcher's leadership style and policies had a lasting impact on the United Kingdom and shaped the country's political landscape.