Boris Johnson has insisted only the Tories will "get Brexit done" and move the country forward while Jeremy Corbyn has vowed Labour will end austerity and give "hope to the next generation".
Jo Swinson has said a strong Lib Dem showing can stop the UK leaving the EU.
Nicola Sturgeon said a vote for the SNP in Scotland could stop a Tory victory.
With voting set to begin at 07:00 GMT on Thursday, the parties are stressing the scale of the choice facing people and the impact it will have on the direction of the country.
The BBC's political editor Laura Kuenssberg said voters were being offered hugely divergent choices when it came to the UK's relationship with Europe, with the Conservatives promising to leave the European Union next month while Labour and others were backing a further referendum.
And the BBC's economics editor Faisal Islam said both the Tories and Labour were proposing fundamental changes to how the UK's economy and trade have worked over the past 30 years.
In terms of the opinion polls, the Conservatives retain a solid lead over Labour, according to the BBC's opinion poll tracker.
A poll produced by YouGov released on Tuesday evening suggests the Conservatives are on course for a small majority of around 28 - but the pollster points out that the margin of error means neither another hung Parliament nor a larger Tory majority can be ruled out.
Labour is hoping for a late swing in its favour, as happened in the 2017 general election, while the Tories are warning about the possibility of a hung Parliament, amid concerns about voter complacency.
Both Conservative and Labour party leaders will be hoping to put a rocky few days behind them, as they embark on the traditional election-eve tour of target seats.