In a surprising admission, Mr Farron made a pitch for voters in former Lib Dem heartlands in the South West, where many people voted to leave the European Union.
Speaking to BBC One's Andrew Marr Show, he said: "I don't want to go off on a little bit of a rabbit hole here, but you will remember that I resigned from the Liberal Democrat front bench about 10 years ago because I am a bit of a Eurosceptic.
"I'm somebody who challenges people in power - the EU, in Government, in councils - but I am somebody who believes Britain is better off in the European Union."
Mr Farron ruled out going into coalition with other parties and dismissed Labour for "fighting amongst themselves".
He also paid tribute to former prime minister Tony Blair, saying: "I have many, very clearly on the record, disagreements with Tony Blair, not least over the illegal and counter-productive war in Iraq.
“But I do admire Tony Blair for one thing in particular, and that is his ability to put together a small-c coalition that was able to win a general election and defeat the Conservatives in 1997.
"I admire progressives - and he is broadly, I guess, a progressive - I admire progressives who are able to win elections, because if you cannot win then you cannot change people's lives."
His comments came after he had urged voters who propelled Tony Blair to Downing Street 20 years ago to back the Liberal Democrats in the General Election, borrowing New Labour's "things can only get better" slogan.
On the eve of the anniversary of the former prime minister's victory, Mr Farron said it "shows what can happen when a party is prepared to make a broad appeal to change Britain's future", in an apparent attack on Jeremy Corbyn.
Mr Farron argued that his party can fill the gap left by Labour's tack left under Mr Corbyn, who is a persistent critic of the Blair years, and now stands for "principle without power".
Mr Blair led Labour to a landslide election victory after 18 years in opposition, modernising the party and famously scrapping clause IV - interpreted as its explicit commitment to socialism - from its constitution.
Mr Farron said: "My message on the eve of that anniversary is this, things can only get better, but this time with the Liberal Democrats. Back us and change Britain's future.
"I am urging those voters, those people who backed Labour in 1997, to come and vote for the Liberal Democrats.
"Labour have comprehensively failed to stand up for our schools, hospitals and our place in the world. They have become too weak, and too divided, to stand up for those who need it most. Power without principle is barren, but principle without power is futile.
"This election is a chance to change the direction of our country, those people who crossed the Labour box 20 years ago should vote for the Liberal Democrats."