Liberal Democrat Tim Farron called for a new wave of council house construction in an effort to kick-start the economy.
Mr Farron used his keynote speech at the party's conference to rally activists to win back the voters who had been left "angry and perplexed" by the Lib Dems' decision to form a coalition Government with the Conservatives.
In an address which won a standing ovation from the Brighton audience, Mr Farron said: "I need us to see this as the moment when the 2015 general election began, when we committed the energy, the time and resources to winning against our opponents.
"You have beaten them once, go out and beat them again."
Defending the coalition, he said: "I didn't join the Liberals to comment on the world, I joined the Liberals to change the world and you don't change things from the luxury of opposition."
Setting out his vision for 250,000 new council homes by 2015, Mr Farron said: "Every week when I go knocking on doors, I can guarantee that before the evening is out I will meet a teacher, a nurse or a copper who will tell me that they have no hope of finding a decent, affordable home.
"All they want is a decent place they can afford in the community that they serve. This is our chance to help, and build ourselves out of recession at the same time.
"It is an immense challenge, but immense challenges require immense ambition.
"Let's commit now to put a roof over the heads of families in need, let's commit now to build 250,000 council houses and let's commit now to doing it by 2015."
In a speech designed to rally the party's activists, Mr Farron hit out at Tory "climate change deniers" and said Labour had wasted its years in power.
Despite the Lib Dems' poor poll ratings, Mr Farron insisted there was still time to win back the voters who have deserted Nick Clegg's party.
He said: "Our liberal vision should not be to win power for the sake of it, but it should be to win power. Let us seek too govern, and govern as liberals.
"If we choose that vision, we would be foolish to write off those voters who have gone off us in the last two years.
"I absolutely refuse give up on them. They may be disappointed, angry, perplexed, but it's up to us to give them a vision, a reason, a passion to return."
Despite Mr Clegg's apology for failing to keep his pledge on tuition fees, the issue has refused to go away for the party.
Mr Farron said the Lib Dems should have fought harder to secure a better deal on fees in the coalition negotiations.
He said the Deputy Prime Minister was "gutsy" for making the apology over tuition fees and described the public reaction to it as "benign and surreal".
When told Mr Clegg was one of the least popular political leaders since Labour's Michael Foot the party president told the Sky News Murnaghan programme: "Well Michael Foot got 28% and 209 seats so we will have that."
Mr Farron, who rebelled over hike in fees, said party could have pushed harder to make the policy a "red line" in the coalition negotiations.
"Personally, I think we should have argued much harder for it in the Coalition negotiations and we should have made sure it was a red line there."
Mr Farron said there would be less pressure on the Lib Dems to sign up to coalition if there was a hung parliament at the next election.
"There is a third option or a fourth option, which is next time round you could have a minority government simply because there would be a fixed term parliament and we know the next election would be another five years away.
"I'm not saying I favour that, I'm just saying we need to remember there are more than two or three options."