Former business secretary Sir Vince Cable has become the first contender to confirm a bid to replace Tim Farron as Liberal Democrat leader.
The 74-year-old said he wanted to use his "energy, enthusiasm and experience" to lead the party through a period of "chronic uncertainty".
The party's elder statesman said he particularly hoped to attract young people "to our cause" with the Conservatives "in disarray and in retreat" and a "complacent" Labour's economic policy set to be "found out".
Sir Vince, who at this month's election regained the Twickenham seat he lost in 2015, is expected to be a frontrunner in the party race after former favourite Jo Swinson dropped out.
Former health minister Norman Lamb and former energy minister Sir Ed Davey are both expected to announce challenges against their former Conservative-Lib Dem coalition colleague.
Former business minister Ms Swinson will instead contest the deputy leadership in a move that reportedly could see her support Sir Vince's bid for the top job.
Sir Vince, himself a former party deputy, said the party had to get prepared for another national vote as he announced his leadership challenge on party forum site Lib Dem Voice.
"With the prospect of another election looming large, we must be ready for the fight," he wrote, as he predicted "big opportunities ahead".
Sir Vince added: "We are now growing again and the political winds are moving in our favour."
Mr Farron quit last week, within days of the General Election, after facing scrutiny over his Christian views.
"To be a political leader, especially of a progressive liberal party in 2017, and to live as a committed Christian, to hold faithfully to the Bible's teaching has felt impossible," Mr Farron said.
The Lib Dems saw their number of seats rise to 12 during the recent election, including Sir Vince's return to a London seat he first won in 1997.
But the party lost former leader and ex-deputy prime minister Nick Clegg on a night of big gains for Labour among the opposition parties.