More than 4,000 polling venues across England, Scotland, Wales and Northern Ireland, including a windmill, several pubs, a hair salon and a chip shop, open their doors at 0700 GMT for a day of voting until 2200 GMT.
All eyes will be on the winter weather, with forecasts of near-freezing temperatures, rain and even snow that could affect turn-out in the first December election in nearly a century.
Up for grabs are all 650 seats in the British parliament, which has been deadlocked since the 2016 referendum on EU membership that saw a majority vote to leave.
Prime Minister Boris Johnson, who took over from Theresa May in July after she was unable to get parliament to approve her EU divorce deal, is hoping to secure both a mandate and a majority.
Johnson’s Conservatives need just nine more seats for a majority, which would allow him to push through his own Brexit deal with Brussels and take Britain out of the bloc by the end of January.
Johnson said Thursday was a chance to end more than three years of political deadlock and uncertainty.
“Just imagine how wonderful it will be to settle down to a turkey dinner this Christmas with Brexit decided,” he said in a final message to voters.
Looking to stop Johnson is the main opposition Labour party.
Victory would make its 70-year-old leader Jeremy Corbyn the first Labour prime minister since Gordon Brown in 2010 and the oldest first-time premier since Viscount Palmerston in 1855.
Corbyn is proposing to renegotiate softer exit terms with Brussels within three months and put them to a new referendum, alongside an option to remain in the 27-member bloc, after a three-month campaign.
A franchise extension would enable millions of EU nationals in Britain to vote in the referendum.
Corbyn said Britain was at a crossroads and the election was “truly historic”.
“Vote for hope. Vote for real change,” he said.
The election features 3,321 candidates — from 18-year-olds to octogenarians — in constituencies covering windswept Shetland off northeast Scotland, to the Isles of Scilly more than 750 miles (1,200 kilometres) away off Cornwall, in southwest England.
The first indication of the overall result will come in an exit poll at 2200 GMT. The first actual result is due from around 2300 GMT. The remainder will trickle in overnight.
Johnson has hammered home his message to “Get Brexit Done” against a backdrop of voter fatigue at the election — the third in less than five years — and the tortuous Brexit process.
But the EU itself has indicated the chances of securing a comprehensive trade deal before a December 2020 deadline is unrealistic.
That would again raise the prospect of Britain facing a “no deal” scenario, plunging business and the British economy into fresh uncertainty.
Corbyn, meanwhile, has had to brush off claims of indecision about his neutral Brexit stance, and claims of anti-Semitism within Labour.
Questions have also been asked about the cost for his radical leftist programme for massive public sector investment and renationalisation of some key sectors.
He has positioned Labour as the only defender of the UK’s cherished state healthcare system that he alleges Johnson wants to sell off in a “toxic” post-Brexit trade deal with US President Donald Trump.
Pollsters YouGov last month predicted that Johnson’s Conservatives would have a comfortable 68-seat majority but on Tuesday indicated that projection been cut to 28.
Brexit has turned traditional political allegiances on their head and shock results could be on the cards, with tactical voting expected along Leave/Remain, rather than party lines.
Labour’s so-called “Red Wall” in northern England — which mainly voted to leave the EU — is being watched closely for Conservative gains, as is north Wales, another traditional bastion of the left.
“There’s more volatility than there ever has been before,” said Chris Curtis, political research manager at YouGov, pointing to an increase in swing voters.
“At this stage, the most likely outcome is a Conservative majority,” he told AFP.
“However, a hung parliament is possible but also a much larger Conservative majority isn’t something that we could rule out.”