Charles Kennedy has called on people to "vote positively" for his party as the last campaign day draws to a close.
The Lib Dem leader held rallies in London, Leeds and Edinburgh
He accused Labour leader Tony Blair of "crying wolf" when he said switching to the Lib Dems would let the Tories in.
"The most optimistic and most positive vote is going to be a vote for the Liberal Democrats," he said, predicting that millions would back his party.
Mr Blair focused on the strong economy, while Tory leader Michael Howard urged voters to choose a "brighter" Britain.
Speaking in Edinburgh at the end of a gruelling month on the campaign trail, Mr Kennedy said people should not believe a vote for his party was wasted.
"The Lib Dem campaign has been the most positive, it's been the most upbeat, the most constructive," he said.
"Let's give the lie to this last-minute desperation from Tony Blair that if you go out and vote Lib Dem, you get Michael Howard as prime minister.
"It's not going to happen and our message to the people of the country is that if you agree with our principles, you support our values, go out and vote Liberal Democrat because what you'll do is elect Liberal Democrat."
At previous campaign stops in Leeds and Brent East, Mr Kennedy highlighted his party's opposition to the Iraq war and repeated pledges to abolish student fees, help pensioners and protect the environment.
Mr Kennedy said support for the Tories had "collapsed" during the course of the campaign.
He has stressed his party can move from third place to win seats and said the election would decide the kind of country British people wished to live in.
Speaking earlier, he said: "Over this parliament, the Liberal Democrats have proven that we can come from third place behind the Conservatives, to beat Labour in their back yard.
"In Brent East one in four voters switched to the Liberal Democrats, and the Liberal Democrats won. In Leicester South one in five voters switched to the Liberal Democrats and the Liberal Democrats won. The Tories were relegated to a very poor third."
He said Mr Blair had "cried wolf one too many times" over the dangers of letting the Tories in and urged voters to "take a stand" by voting Lib Dem.
A smaller Labour majority would result in a "healthier" Parliament, Mr Kennedy said, "where one party does not ride roughshod over its own people, never mind other political parties".
The Lib Dems are not forecasting how many more seats they can win - they say they genuinely do not know - but Mr Kennedy said it was clear they could gain "significantly more" than last time.
"We set no ceiling on our ambitions as a party. We are clearly set for a further major advance on Thursday.
"But I am determined this will not be the high watermark of Liberal Democrat or electoral success. It will be a further staging post - an important staging post - in our upward progress as a party."