when was margaret thatcher prime minister

Margaret Thatcher was Prime Minister of the United Kingdom from May 4, 1979, to November 28, 1990. She served three consecutive terms during this period, making her the longest-serving British prime minister of the 20th century and the first woman to hold the office. She was leader of the Conservative Party from 1975 until 1990 and won general elections in 1979, 1983, and 1987 before resigning in 1990.