Jo Swinson, the leader of Britain's Liberal Democrats, said on Tuesday the party would "revoke Article 50 on day one" if it were to win the next general election.
"Today I am standing here as your candidate for Prime Minister," Swinson told the conference in Bournemouth — the first since she was elected leader.
You can watch her speech in the video player, above.
"The tired, old, parties have failed, looking inwards at a time of national crisis," she said.
"The first task is clear: we must stop Brexit," she continued, adding: "A Liberal Democrat majority government would revoke Article 50 on day one."
The Liberal Democrats joined forces earlier this month with the main opposition Labour party, Scotland's National Party (SNP), Wales' Plaid Cymru and the Green party to pass legislation to ensure Prime Minister Boris Johnson could not take the country out of the European Union without a deal on October 31.
Together, they also inflicted another bruising defeat on Johnson by rejecting his call for an early general election until after the anti-no-deal bill had become law.
But on Tuesday, Swinson didn't pull any punches on either Johnson or Corbyn saying the country deserves "a better choice than an entitled Etonian or a 1970s socialist".
She criticised Johnson's affirmation that he could negotiate a new deal in a matter of weeks, saying: "Yesterday he failed to negotiate whether to have a press conference."
"It's clear he's determined when it comes to crashing us out without a deal," she continued.
Turning to Corbyn, she said that "if he had campaigned to remain in 2016 with half of the energy he put in the 2017 election, we may have seen a different result" and condemned his position to take the country out of the EU if Labour were to win the next general election.
"(Brexit Party leader) Nigel Farage might be Brexit by name, but it is very clear that Jeremy Corbyn is Brexit by nature," she continued.
Boasting about the party's recent successes — seven new MPs have joined its ranks in the last few months — Swinson said they were now facing "the fight of our lives for the heart and soul of Britain."
The next general election — which has yet to be agreed upon but is expected take place within weeks of the October 31 Brexit deadline — will be crucial to determine "what kind of country we are".
"Whether we want to tackle our biggest challenges with our closest allies, or on our own; whether we welcome those who want to build a better life in our country, or shut the door on them; whether we ensure every single child can go on and fulfil their dreams," she stated.
Beyond Brexit, Swinson laid out climate change and wellbeing as a key topic in the party's manifesto, announcing that a "wellbeing budget" modelled on the one launched in new Zealand earlier this year.
A YouGov poll released last week credited the Liberal Democrats with 19% of voting intention, behind Labour and the Conservatives with 23% and 32% respectively.