Veteran Labour MP Harriet Harman has announced she will stand down at the next general election.
She revealed her decision in an email to her local party in Camberwell and Peckham on Tuesday morning after almost 40 years as their MP.
She promised to "work energetically" until the next polling day.
But Ms Harman said she would then leave the Commons "now confident that Labour is gaining strength under the leadership of Keir Starmer".
Labour MP Karen Buck called her a "guiding light and inspiration for women in politics", while former MP and now West Yorkshire Mayor, Tracey Brabin, called her "the original glass ceiling smasher".
The 71-year-old became an MP in 1982 and has held a raft of posts in the party - including two brief stints as leader after Gordon Brown and Ed Miliband stepped down.
She served as deputy leader for both men, but is perhaps better known for her feminist campaigning in Parliament and as Mother of the House - the woman with the longest continuous service in the Commons.
In her email, Ms Harman said when she entered Parliament, she was one of just 11 female Labour MPs in a Commons that was 97% male.
"Now there are 104 Labour women and across all parties women MPs are a 'critical mass'," she added.
"But there remains much more to be done till women genuinely share political power with men on equal terms and until women in this country are equal.
"I will leave the House of Commons with my feminism, my belief in Labour and my enthusiasm for politics undimmed."
Ms Harman took to Twitter to share some facts and figures about her time in Parliament.
As well as fighting 10 general elections, she has served under seven prime ministers and eight Labour leaders.
She has spoken in the Commons 9,850 times since November 1982.
And she became a mother of three and grandmother to five.
MPs have been paying tribute to Ms Harman, with shadow health secretary Wes Streeting calling her a "trail-blazer, change-maker and champion".
His party colleague and shadow minister Jess Philips said: "All my life Harriet has been in Parliament and as a woman that life would have been very different if she hadn't.
"Harriet Harman is my hero. I owe her a debt so big it cannot be repaid."
And Labour's Liz Kendall added: "Harriet Harman has inspired so many of us in politics, and has blazed a trail for women and equality.
"Parliament won't be the same without her but we will keep fighting the good fight!"