Former Liberal Democrat leader Sir Vince Cable is to step down as an MP at the next general election.
Sir Vince has represented Twickenham since 1997 and served as business secretary in the coalition government.
After losing his south-west London constituency seat at the 2015 general election, the 76-year-old regained it in the snap poll two years later.
In a statement, he said it had been "an honour" to serve as Twickenham's MP and as a leader of the party.
Sir Vince said he had intended to represent his constituents until May 2022, the scheduled date for a general election, but he decided now was the best time to step down to allow another candidate, who could serve past 2022 to prepare for a possible autumn election, "if Boris Johnson decided to cut and run".
Sir Vince who took over the Lib Dem leadership from Tim Farron, warned of "major battles in the next few weeks to stop a damaging Brexit".
Under his leadership the Lib Dems witnessed a grassroots revival with the party taking control of a host of councils during May's local elections.
He was replaced by East Dunbartonshire MP Jo Swinson after she defeated Sir Ed Davey in a leadership election last month.
A Liberal Democrat spokesman said: "Vince has enjoyed a fantastic parliamentary career in the Liberal Democrats and representing the people of Twickenham.
"He will continue to serve as the MP until the next election, whenever that may be."
Karl Mercer, BBC London Political Correspondent
Sir Vince's seat will be eyed by many a budding Lib Dem MP and at the last election they won it with a majority pushing 10,000.
It's a place that chimes heavily with the party's pro-remain stance on Brexit - at the 2016 referendum two-thirds voted in favour of staying in the EU.
It would seem to be tailor-made for one of the party's new stars; former Labour MP Chuka Umunna, who left his party over its Brexit stance and is now the Lib Dem spokesperson on foreign affairs.
A devoted Remainer, a good media performer and a London MP to boot, he would seem to be an ideal fit.
But buyer beware! He would do well to remember that Twickenham has not always been so kind to the Lib Dems in recent years.
Sir Vince lost the seat to the Conservatives in 2015, when the Lib Dems were left with just one MP in the capital.
In a bid to ensure candidates were in place in the event of a snap general election, the Lib Dems sent emails on Wednesday to prospective parliamentary candidates about replacing Sir Vince in Twickenham.
When he became leader in 2017, he was the oldest person to be appointed head of a major party since Winston Churchill.
Sir Vince, a one-time Labour Party member and ex-economics lecturer, appeared on the Christmas edition of BBC One's Strictly Come Dancing in 2010.
He was knighted in David Cameron's 2015 dissolution honours in recognition of his services to political and public life.
A grandfather, he is married and has three children.