Voters will go to the polls in a by-election sparked by Sadiq Khan's victory in the London mayoral election.
The new mayor secured a majority of 2,842 for Labour in Tooting at the general election but vacated the seat in May after heading to City Hall.
Labour councillor and junior doctor Rosena Allin-Khan is battling to hold the London constituency for her party against Conservative Dan Watkins.
The by-election will be closely watched by Jeremy Corbyn's critics in the Labour Party, but coming a week before the EU referendum, the contest has been overshadowed by the closing stages of the Brexit battle.
Born and raised in the area, Dr Allin-Khan works as an emergency doctor at St George's Hospital and is also deputy leader of Wandsworth Labour group.
Mr Watkins, a local businessman, gave Mr Khan a close fight at the 2015 general election.