A motion passed at the party’s conference in Bournemouth says a Lib Dem majority government would be "recognised as an unequivocal mandate to revoke Article 50 and for the UK to stay in the EU".
Party leader Jo Swinson pledged to cancel Brexit altogether if the Lib Dem revival, fuelled by the defection of six MPs, propels her into Downing Street.
"If the Liberal Democrats win a majority at the next election, if people put into government, as a majority government, the 'Stop Brexit' party, then stopping Brexit is exactly what people will get,” Ms Swinson told the BBC’s Andrew Marr show ahead of the vote.
The East Dunbartonshire MP added: "We have argued that a specific Brexit deal should be put to a People's Vote to give clarity.
"We still argue for that. But if we end up at a general election then I think we need to be straight forward with people and give them an option for all this Brexit chaos to stop.
"I recognise not everyone agrees with the Lib Dems on this. (But) it is genuinely what we think is right for the country."
Speaking in the debate at Bournemouth, Edinburgh West MP Christine Jardine said the policy meant the Lib Dems had “faith in the people”.
“Do we want a referendum? Yes we do,” Ms Jardine said. “If there’s a deal to put to the people, we do still want a referendum, and we we would win it - but we are running out of time.
“If there is a general election, and the people vote for us, and give us a majority, that will be the will of the people, because the people will have voted knowing that we, in a majority government, will vote to revoke Article 50.
“So let's have faith in the people to vote for us to put Jo Swinson in Number 10 so she can revoke Article 50 - and then we can say, yes, we stopped Brexit.”
Former Liberal Democrat leader Sir Menzies Campbell told the conference it "grieves him" that the union of the UK and the UK's membership of the EU should be at risk because of "nationalism".
Ms Swinson also went on the attack against Boris Johnson and Jeremy Corbyn, saying she wouldn’t help put the Labour leader into power.
"Boris Johnson and Jeremy Corbyn are not fit to be prime minister. We see that day in, day out," she told the BBC.
"Jeremy Corbyn is not going to be put into Number 10 with Lib Dem votes because he is not fit for the position. The country deserves better."
James Cleverly, chairman of the Conservative Party, claimed the Lib Dem stance on Brexit would lead to "more delay, division and uncertainty".
"Despite calling herself a 'democrat', Jo Swinson's mask has slipped and we now know that she wants to overrule one of the largest democratic votes in British history, cancelling Brexit," he said.