Jeremy Corbyn will say that Labour offers a "vote for hope", while Boris Johnson will say the Tories were the only party who can "get Brexit done", reported the BBC.
Liberal Democrat leader Jo Swinson will also call on people to back her candidates to stop the UK leaving the EU.
Polls in the UK will open at 07.00 GMT on Thursday and close at 22:00.
Scottish National Party (SNP) leader Nicola Sturgeon is also expected to be making her final pitch to voters, as the six-week campaign enters its critical final hours.
In terms of the 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.
Their poll puts the Conservatives on 43 per cent, which their model translates into 339 seats; Labour on 34 per cent with 231 seats; the Liberal Democrats on 12 per cent with 15 seats; the Greens with 3 per cent and one seat and the Brexit Party on 3 per cent with no seats. The SNP are projected to have 41 seats, an increase of six on 2017, and Plaid Cymru are unchanged with four seats.
A similar YouGov analysis last month had the Conservatives ahead of Labour by a bigger margin, with a Tory majority of 68.
But the pollster points out that its seat share estimates come with some uncertainty, and the margin of error could put the Tories' final seat numbers between 311 and 367, meaning neither another hung Parliament nor a larger Tory majority can be ruled out.
Fieldwork was conducted between 4 and 10 December, with 100,000 people polled.
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 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.
Boris Johnson is expected to start Wednesday doing a milk round, and will use events throughout the day to stress key Tory pledges on investing in the National Health Service, raising the number of police officers and bringing in a new immigration system.
But his main message will be on Brexit, saying "unless we get out of this quicksand... our future as a country remains uncertain".
Corbyn will begin in Scotland before heading to the north-east of England - - where the Tories are targeting Leave-voting Labour seats - - to appeal to undecided voters.
( With inputs from IANS )