The Lib Dems are styling themselves as the party of the 48 percent who voted last year to remain in the European Union.
Sitting a distant third place in opinion polls ahead of the June 8 vote, the Lib Dems are styling themselves as the party of the 48 percent who voted last year to remain in the European Union.
"We are giving the people of this country the chance to decide on what comes next with Brexit," party leader Tim Farron told Sky News.
"And if the deal that (Prime Minister) Theresa May comes back with is not good enough for you and your family, you should have the right to reject it and to vote to remain," he added.
The Lib Dems pledge to hold a referendum on the final Brexit deal following two years of negotiations between London and Brussels, giving voters the chance to reject the agreement and stay in the European Union.
The party also promises to keep Britain in the European single market and continue freedom of movement, both of which have been ruled out by May.
The prime minister's Conservative Party has surged in the polls in recent months, currently leading with 49 percent of the vote according to a YouGov poll published on May 12.
The main opposition Labour party has 31 percent while the Lib Dems lag behind on nine percent, according to the survey of 1,630 people.
The Liberal Democrats nosedived in the 2015 election after five years as the minor coalition partner alongside the centre-right Conservatives, but they are hoping to regain voters with their pro-Europe promises.
Such a stance helped the party gain its ninth MP in the 650-seat parliament in a December by-election, beating the eurosceptic Conservative candidate by running a strongly anti-Brexit campaign.
In its manifesto the Lib Dems also pledge to guarantee the rights of EU staff working in social care and for the National Health Service, in addition to boosting funding to these areas by £6 billion (£7.8 billion, 7 billion euros).
The extra cash will be raised by increasing income tax by one percent, while the Lib Dems also plan to reverse the Conservatives' cuts to corporation tax.
Legalising cannabis, restricting junk food advertising to children, and suspending the use of bee-harming insecticides called neonicotinoids are also featured in the party's manifesto.