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For Johnson, whose brief tenure in power has been marked by chaotic scenes in Parliament and stark division on the streets over Britain's tortuous departure from the European Union, the victory is vindication.
Educated at the country's most elite school and recognisable by his bombastic style, the 55-year-old must not only deliver Brexit, but also convince Britons that the contentious divorce, which would lead to lengthy trade talks, is worth it.
A decisive win for the Conservatives would also mean disappointment for the millions of people who voted to remain in the EU in a 2016 referendum and who dared to hope the result might be overturned thanks to gridlock in Westminster.
An exit poll showed the Conservatives winning a landslide 368 seats, more than enough for a comfortable majority in the 650-seat parliament and the biggest Conservative national election win since Margaret Thatcher's 1987 triumph.
"I hope you enjoy a celebration tonight," Johnson told supporters in an email. "With any luck, tomorrow we’ll be getting to work."
If the exit poll is accurate and Johnson's bet on a snap election has paid off, he will swiftly ratify the Brexit deal he struck with the EU so that the United Kingdom can leave on January 31 - 10 months later than initially planned.
But nearly half a century after joining what has become the world's largest trading bloc, Johnson faces the daunting challenge of building new relationships and preserving Britain's place as a global trading hub.
The exit poll showed the Conservatives would win a landslide of 368 seats - more than enough for a very comfortable majority in the 650-seat parliament and the biggest Conservative national election win since Margaret Thatcher's 1987 triumph.
Labour were forecast by the poll to win 191 seats, the worst result for the party since 1935. The Scottish National Party would win 55 seats and the Liberal Democrats 13, the poll said. The Brexit Party were not forecast to win any.
"That would be a phenomenal victory for the Conservative Party and Boris Johnson will feel completely vindicated with the gamble that he took," said John Bercow, the former speaker of the House of Commons. "That would be an absolutely dramatic victory."
Official results will be declared over the next few hours.
In the last five national elections, only one exit poll has got the outcome wrong - in 2015 when the poll predicted a hung parliament when in fact the Conservatives won a majority, taking 14 more seats than forecast.
The Labour Party, led by veteran campaigner Jeremy Corbyn, had offered a second referendum and the prospect of the most radical socialist government in British history.
John McDonnell, the second most powerful man in the Labour Party, said the election had been dominated by Brexit which has divided the country since 2016.
"What's clearly come through I think in these results is that this was the Brexit election," he said. "We were hoping a wider range of issues would cut though and have a debate, I don't think that has been the case."
The exit poll was produced by three broadcasters - the BBC, ITV and Sky - who teamed up to jointly produce similar surveys in the last three elections, held in 2010, 2015 and 2017.
In 2010 and 2017, their exit polls accurately predicted the overall outcome and were close to forecasting the correct number of seats for the two main parties.
BREXIT FAR FROM OVER
Thursday's election pitched two of the most unconventional British politicians of recent years against each other. Both have been repeatedly written off by opponents and both offer starkly different visions for the world's fifth-largest economy.
The majority will allow Johnson to lead the United Kingdom out of the club it first joined in 1973.
But Brexit is far from over: he faces the daunting task of negotiating a trade agreement with the EU, possibly in just 11 months. The outcome of the negotiations will shape the future of Britain’s $US2.7 trillion economy.
After January 31, Britain will enter a transition period during which it will negotiate a new relationship with the remaining 27 EU states.
This can run until the end of December 2022 under the current rules, but the Conservatives made an election promise not to extend the transition period beyond the end of 2020.
A large majority could give him the political security to extend the trade talks beyond 2020 because he could overrule the Brexit hardliner European Research Group (ERG) faction inside the party.
"With a big majority BJ can ignore ERG and go for a softer Brexit if he wishes," said Charles Grant, director of the Centre for European Reform.
Johnson called the first Christmas election since 1923 to break what he said was the paralysis of Britain's political system after more than three years of crisis over how, when or even if to leave the EU.
The face of the "Leave" campaign in the 2016 referendum, Johnson fought the election under the slogan of "Get Brexit Done", promising to end the deadlock and spend more on health, education and the police.
He was helped early in the election by the Brexit Party which stood down hundreds of candidates in a bid to prevent the pro-Brexit vote from being split.
While Brexit framed the election, the tortuous exit from the EU has variously fatigued, enthused and enraged voters while eroding loyalties to the two major parties.
The exit poll suggests Johnson's strategy had breached Labour's so-called "Red Wall" of seats across the Brexit-supporting areas of the Midlands and northern England where he cast his political opponents as the out-of-touch enemies of Brexit.
France's European Affairs Minister Amelie de Montchalin said Europe would have clarity if the exit poll was accurate.
"The most important with Brexit is not the way we divorce, it's what we build afterwards," she told reporters in Brussels.
Johnson, the New York-born former mayor of London, became prime minister in July this year. His predecessor, Theresa May, resigned after failing to get parliamentary backing for her Brexit deal with the EU and then losing her party's majority in a snap election.
He defied critics by striking a new deal with the EU but was unable to navigate the maze of a divided British parliament and was defeated by opponents whom he portrayed as subverting the will of the people.
The United Kingdom voted 52%-48% in 2016 to quit the EU. But parliament has been deadlocked since May's failed bet on a 2017 snap election over how, when and even whether to leave.
Corbyn, once an opponent of the EU, said he would remain neutral if he was a prime minister overseeing another referendum. He pledged to overthrow a "rigged system" he said was run by billionaires and tax dodgers.