Milestones in the life of Margaret Thatcher Associated Press Copyright 2013 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Updated 8:51 am, Monday, April 8, 2013 Becomes education secretary. Elected leader of the Conservative Party. Wins national elections, becomes prime minister. Becomes Britain's longest continuously serving prime minister of 20th century. Becomes Baroness Thatcher of Kesteven, a member of the unelected House of Lords with a lifetime title. Ends public speaking after suffering a series of small strokes.