The first woman to serve as chairperson of a major political party in the UK was Margaret Thatcher, who became leader of the Conservative Party in 1975. Thatcher's leadership profoundly transformed British politics, leading her to become the first female Prime Minister in 1979. Her tenure is marked by radical economic policies known as Thatcherism, emphasizing deregulation, privatization, and reducing the power of trade unions, leaving a lasting legacy on British governance.