Sir Vince Cable will quit as leader of the Liberal Democrats in May to make way for a “new generation.”
Cable told party members that unless parliament “collapsed” into an early general election, a leadership contest would be called in May.
The 75-year-old, who became leader in July 2017, said his time leading the party was a “great privilege.”
He said: “I inherited the leadership after two difficult and disappointing general elections.
“But I take pride in seeing the party recovering strongly, with last year’s local election results the best in 15 years, record membership and a central role in the People’s Vote campaign.”
The former business secretary said it was important to have an “orderly, business-like, succession” in contract to the power struggles in the other parties.
Deputy leader Jo Swinson, former energy secretary Ed Davey and education spokeswoman Layla Moran have all emerged as candidates to succeed Cable.
In September, Cable said he would quit once the “Brexit story” was over.
In a statement to party members tonight he said: “This has been a dramatic week in Parliament with Theresa May’s Brexit proposals heavily defeated, and a very clear statement that a ‘no deal’ Brexit must be avoided.
“It is now clear that Brexit will be postponed, and very possibly stopped.”
He said continue to work with the party and his successor "long after" his leadership ends in May.