Former Tory MP Sam Gyimah says his new party will still be campaigning for a second referendum – despite its plans to make cancelling Brexit its main policy on Europe.
He was sacked from the Conservative party for rebelling to vote take a no-deal Brexit off the table.
Members of the anti-Brexit party are expected to back a move during their conference in Bournemouth to write the revoking of Article 50 into its manifesto for the next election.
But the former Conservative minister said the Lib Dem policy would only come into play if it won a general election outright.
With the Lib Dems polling anywhere between 16 and 20%, the party could be a kingmaker in any future coalition rather than the largest party in its own right.
Speaking on Sky News’s Sophy Ridge On Sunday from the party conference, Mr Gyimah said: “The position is, if the Liberal Democrats were to win a general election their policy would be to revoke Article 50.
“Revocation would be on condition that the British public have overwhelming voted for a Lib Dem government.
“If you vote for a government, you would say they should implement their policy and that is what they would be doing.
“The party is still supporting a People’s Vote as a way to break the Brexit deadlock. If you want to resolve Brexit, the best way is to have a People’s Vote’now that we all know what is negotiable.”
The former aide to David Cameron said the Conservative Party no longer stood for "liberal values".
He said it "became very clear" during the Tory leadership contest, which he stood in, that there were not enough moderate MPs left in the party.
"It has done something unprecedented - it has withdrawn the whip from moderate MPs," Mr Gyimah said.
"The stark reality is that I had to face up to the fact that the Tory Party is in a different place.
"If I want to stand up for liberal values, then the Conservative Party is no longer the place to do that."
Chuka Umunna, who defected from Change UK to the Lib Dems, welcomed Mr Gyimah to the party, but said the Tories have become a "right-wing, populist, nationalist party".
Speaking to Sophy Ridge On Sky, he said: "The ejection of 21 Conservative MPs including Sam Gyimah, who we are incredibly happy to now have in the Liberal Democrats, wasn't just an ejection of heavyweights, substantial individuals who command respect across the House of Commons, you actually saw the ejection of an entire tradition, the one nation Disraeli tradition, from the Conservative Party."
Mr Umunna said another Tory defector Dr Phillip Lee, who has been criticised for failing to vote in support equal marriage, has liberal values and is an important part of the party.
He said both Labour and the Tories "as they are currently configured" are not parties the Lib Dems could currently work with.
Mr Gyimah said there was “every chance” he could fight his current seat of East Surrey at the next election.
He secured a majority of almost 24,000 votes for the Tory Party at the snap election under Theresa May’s leadership two years ago.
“Since 2017, public opinion has shifted since then,” he said. “But there will be an election, as we all know, very soon and I will decide what I will do then.
“A lot has happened in a short space of time and those discussions are yet to come.”
For any MP to defect to the Lib Dems, the local constituency parties must first agree, meaning Mr Gyimah is being backed by Liberal Democrats in East Surrey.