Jo Swinson says that a Liberal Democrat government would revoke Article 50 and stop Brexit if it can win a majority at the next UK election.
At the party conference, delegates voted to cancel Brexit in the event that it wins a national election, strengthening their anti-Brexit position.
Party leader Swinson wants to win more than 350 seats in Parliament—up from a current tally of 18—and use it to stop Brexit.
Speaking on the BBC’s Andrew Marr show Sunday before the conference vote, Swinson said: “We’re going to fight for a Liberal Democrat majority government and for me to be prime minister of the country.
“We’re in such dangerous times and we have an opportunity to change the course but that does require the Liberal Democrats to make that leap and I'm determined to build that.
“If the Liberal Democrats win a majority, if people put into government the stop Brexit party, then stopping Brexit is exactly what people will get. Yes, we will revoke Article 50.”
Swinson, who was elected leader earlier this year, said that Boris Johnson and Jeremy Corbyn were “not fit to be prime minister”. She has already seen a number of defections from the Conservative and Labour parties in recent weeks, including Tory rebel Sam Gyimah.
Conservative MP Phillip Lee defected to the party on the eve of a crucial vote two weeks ago on a bill to compel Johnson to seek an extension of the Brexit deadline beyond October 31. From Labour, Luciana Berger and Chuka Umunna also recently joined the Liberal Democrats.
But Swinson has a mountain to climb if she is to secure the surge that she wants for the Liberal Democrats. She has a slim majority in her constituency seat of East Dunbartonshire, which she lost to the Scottish National Party in 2015.
Swinson was able to win back the seat in the snap election called by Theresa May in 2017, but faces a renewed challenge from the anti-Brexit SNP in the next election.
Her new recruits may also struggle: Although Gyimah won East Surrey in 2017 with a majority of 23,914 and almost 60% of the vote, 54.2% of voters in the constituency voted to leave in the 2016 referendum. He will now have to win as a representative of an openly anti-Brexit party.