But just two years on, Johnson’s once seemingly unassailable position is looking shaky after a series of scandals have left his credibility in tatters.
In opinion polls and even among members of his ruling Conservative party, there is open talk that he should quit - or be forced out by an internal vote of no confidence.
“So far he’s been Teflon. Virtually nothing has touched him,” Robin Pettitt, a specialist in British politics, told AFP.
But he said a succession of scandals and sleaze allegations “adds up over time”.
“There’s been so many of them that eventually it’s going to overflow,” he added.
There has been mounting public anger at reports that Johnson’s staff broke coronavirus rules last year by holding a Christmas party in Downing Street at a time when the public were told to cancel their festive plans.
Johnson’s repeated denials of wrongdoing, however, have failed to convince, after video footage emerged of his staff apparently joking that they knew it was a breach.
The situation is “blatant”, said Pettitt. “It’s so obviously wrong for the makers of the rules to be breaking them, especially at Christmas.”
With his mop of unruly blond hair and ill-fitting suits, Johnson has long played up to his image as an unconventional politician. But it has been effective.
His simple Brexit pitch won over voters in the heartlands of the main opposition Labour party in northern England, giving him a whopping 80-seat majority in parliament.
Even after a much-criticised start - and a still staggeringly high COVID death toll and infection rate - he has enjoyed a bounce from a successful vaccination campaign.
But his characteristic bluster does not seem to be enough this time.
A YouGov poll for The Times yesterday (Dec 10) suggested 68% of respondents believed he was lying when he denied the rules were broken.
And his overall popularity has plunged to an all-time low in other polls, showing Labour in a rare lead.
Political scientist Steven Fielding said that, with the new Omicron strain threatening Britain, Brexit not as “done” as he claims and the economy stumbling, Johnson is not in a good place.
“At this very moment, this is when people look at Boris Johnson and think, ‘you’re a liar, you’re not telling the truth’ - just when he needs to be seen as a leader, someone that we can trust, someone who is dealing with things in our interests,” said Fielding, from the University of Nottingham.
Johnson, 57, who has just become a father for the seventh time, has long been accused of bending the truth.
As a fledgling journalist, he was sacked from The Times for making up a quote. He went on to peddle “euromyths” as Brussels correspondent for the Daily Telegraph.
But if the public were prepared to overlook his bumbling eccentricities, they may be less forgiving of claims of dodgy dealing and cronyism.
An inquiry this week fined Johnson’s Tory party for failing to declare who paid for the lavish refurbishment of his Downing Street flat - a scandal dubbed “cash for curtains”.
He has also been condemned for trying to change parliament’s disciplinary procedure after Tory MP Owen Paterson was caught lobbying ministers illegally and quit.
According to Pettitt, Johnson’s supporters have tolerated his style as long as he has delivered.
But he warned: “If he starts to look like he’s not a winner, then they’ll fall out of love with him very quickly.”
A key test of that comes next Thursday, at a by-election in Paterson’s old North Shropshire constituency in central England.
A loss in the Tory safe seat plus a sizeable rebellion from his own MPs against the government’s new COVID restrictions could see the calls for Johnson to go get even louder.
Even one of Johnson’s staunchest media allies, The Telegraph, allowed Labour leader Keir Starmer to use its pages to say he was “unfit for office”.
Experts - and bookies - are predicting a leadership challenge in the weeks or months to come.
“The Conservative party have always been very ruthless when it comes to getting rid of leaders that were not working,” said Pettitt.
There is no shortage of candidates: finance minister Rishi Sunak and Foreign Secretary Liz Truss are popular with grassroots.
But Fielding said: “The problem is who replaces him [who] can... replicate the appeal that he had for those former Labour voters.”