Beckett trained as a scientist, graduating from the Manchester College of Science and Technology, and worked as a metallurgist at the University of Manchester. She became active in the Labour Party and was elected to the House of Commons (Commons, House of) in October 1974. The following year she became a government whip, and in 1976 she was named parliamentary undersecretary for the Department of Education and Science.

Beckett lost her seat in the House of Commons in 1979, after which she became a researcher with Granada Television. She remained politically active, however, and served briefly on Labour's National Executive Committee. Beckett was returned to the House of Commons in the 1983 general election. Between then and the Labour Party's return to office in 1997, she held several posts in the shadow cabinet. In 1992, following Labour's fourth consecutive general-election defeat, Beckett was elected deputy to the new leader, John Smith. She rose to party leader in May 1994 when Smith died suddenly, but she held the post for just 10 weeks, losing the subsequent leadership election to Tony Blair (Blair, Tony) and the deputy leadership to John Prescott. Beckett was the first woman deputy leader and the first woman leader of the Labour Party.

In 1997, after Labour returned to government, Blair appointed Beckett president of the Board of Trade and secretary of state for trade and industry. The following year she became leader of the House of Commons, and in 2001 Beckett became secretary of state for environment, food, and rural affairs. In the latter post Beckett was actively involved in global climate change, acquiring a reputation as a skillful negotiator. This talent, together with her firm loyalty to Blair, prompted him to promote Beckett to foreign secretary in May 2006.

Beckett's tenure as foreign secretary was dominated by the continuing Iraq War, Iran's refusal to halt its nuclear program, and the battle between Israel and Hezbollah in Lebanon in 2006. Shortly after Blair resigned as prime minister in 2007, Beckett was replaced as foreign secretary by the new administration of Gordon Brown (Brown, Gordon). The following year Beckett returned to government when Brown appointed her minister for housing and planning.