Jo Swinson or Sir Ed Davey will be named as the next leader of the Liberal Democrats later, replacing incumbent Sir Vince Cable.
The result of the pro-EU party's leadership contest is expected at around 16:00 BST on Monday.
Ms Swinson, the MP for East Dunbartonshire, has been the party's deputy leader for two years and is the bookmakers' favourite.
She is up against ex-energy secretary Sir Ed, MP for Kingston and Surbiton
Both candidates are backing another EU referendum.
The Liberal Democrats began the process of choosing their next leader in May, as Sir Vince - who has served as leader since July 2017 - announced he would be handing over a bigger, stronger party .
Under Sir Vince, the Lib Dems have been at the forefront of the campaign for another EU referendum as a means of stopping Brexit.
The party now has 12 MPs and won 20% of the vote share in the European elections.
In the English local elections in May, they were the biggest winners of the night.
Media playback is unsupported on your deviceMedia captionLiberal Democrat leadership: Ed Davey and Jo Swinson
Ms Swinson has previously suggested that the election of Boris Johnson as Tory leader could be an excellent recruiting tool for the Lib Dems.
She believes Mr Johnson - the favourite to replace Theresa May - would be disastrous as PM, but a silver lining would be that it would be good for her party.
The result of the Tory battle for Number 10 will be announced on Tuesday.
Meanwhile, setting out his pitch, Sir Ed previously said the UK needs a new economic model and making capitalism turn green so Britain is a world green finance capital .
That means being tough on our banks, on the stock exchange, on the pension funds, so they take account of climate risk.