Former Conservative Zac Goldsmith will try to see off a Liberal Democrat challenge as he fights to retain the parliamentary seat he quit in protest over airport expansion when voters go to the polls.
The former Tory London mayoral contender, who is standing as an independent, is going head to head with Sarah Olney in the Richmond Park by-election.
Lib Dems have poured resources into the contest, which they believe gives voters a chance to deliver a verdict on Brexit.
In the final hours of campaigning, the party hit the streets with Bob Geldof, who attacked Mr Goldsmith, an old friend, for being a failure and chanted "Zac is crap" while posing for pictures.
The singer joined Ms Olney, an accountant working at the National Physical Laboratory in Teddington, who joined the party in May 2015, to chat to voters.
Neither the Tories nor Ukip is fielding candidates to stand against Mr Goldsmith, who secured a 23,000 majority from the 2015 general election.
Some Labour MPs urged their party to avoid contesting the by-election to give the Lib Dems a better chance of winning, but writer, broadcaster and railway historian Christian Wolmar is representing the party.
The Greens, who called for a ''progressive alliance'' against Mr Goldsmith, are not fielding a candidate.
Eight candidates are contesting the seat, including Fiona Syms, the ex-wife of Tory MP Robert Syms (Poole). She is standing as an independent opposed to Mr Goldsmith but has said she will seek to join the Conservatives if she is elected.