On 24 March 2017, Dame Margaret Beckett MP became the longest serving female MP, serving for 38 years and 128 days, in two separate periods.
Margaret Beckett (or Margaret Jackson, as she then was) was first elected as the MP for Lincoln at the general election held on 10 October 1974. She lost her seat at the following election (3 May 1979) but returned to the House of Commons on 9 June 1983 as MP for Derby South. She has continued to represent Derby South since then.
On 24 March 2017 she overtook Gwyneth Dunwoody as the female MP with longest total service since women were first elected to the House of Commons in 1918.
Gwyneth Dunwoody served as an MP from 31 March 1966 to 18 June 1970, and then continuously from 28 February 1974 until her death on 17 April 2008. Her total service amounted to 38 years and 128 days. Earlier in the year, Gwyneth Dunwoody’s record of longest unbroken service by a woman MP was beaten by Harriet Harman (see Harriet Harman record breaker! on this blog).
Since 1918, 456 women have been elected to the House of Commons. When Margaret Beckett was first elected in October 1974, she was one of six female MPs elected for the first time. Prior to October 1974, 100 female MPs had been elected.
She became Deputy Leader of the Labour Party in April 1992. She served as acting Leader between May and July 1994, following the death of John Smith.
In May 1997, Margaret Beckett was one of five women appointed to Tony Blair’s first Cabinet. In May 2006, she became the first (and still the only) woman to serve as Foreign Secretary.
Before 1997, just ten women had served in Cabinet since 1929, when Margaret Bondfield became the first women to be a Cabinet minister. Following appointments to Theresa May’s Cabinet in July 2016, the total number of female Cabinet ministers, since 1929, now stands at 43.
In December 2015, Dame Margaret Beckett was chosen by the Joint Committee on the National Security Strategy to be its Chair.
Richard Kelly, Parliament & Constitution Centre, House of Commons Library
 Gwyneth Dunwoody’s total service also amounts to 38 years and 128 days but because of the way leap years fall, her service amounted 14,007 days. On 24 March 2017, Dame Margaret Beckett marked her 14,008th day as an MP.
 The other four women were Harriet Harman, Mo Mowlam, Clare Short and Ann Taylor.