Boris Johnson is preparing to take over as prime minister and begin assembling his new cabinet, after being named the new Conservative Party leader earlier today.
The former London mayor will fulfil his long-held ambition of residing in 10 Downing Street tomorrow, after beating rival leadership candidate Jeremy Hunt.
Mr Johnson said it was an "extraordinary honour and privilege" to be elected Tory leader and pledged to "energise the country" following the announcement.
"The campaign is over and the work begins," he added.
He also paid tribute to outgoing prime minister Theresa May, thanking her for her "extraordinary service to this party and this country".
And Mr Johnson described his leadership opponent Mr Hunt as a "font of excellent ideas".
The incoming prime minister has already appointed one of the most key roles, elevating long-serving whip Mark Spencer to the person in charge of Tory discipline in his administration.
Mrs May pledged her support to her successor, posting on Twitter: "We now need to work together to deliver a Brexit that works for the whole UK and to keep Jeremy Corbyn out of government.
"You will have my full support from the back benches."
Mr Hunt paid tribute to Mr Johnson's "optimism, energy and unbounded confidence in our wonderful country", while Donald Trump became the first foreign leader to congratulate the incoming prime minister.
The US president tweeted: "Congratulations to Boris Johnson on becoming the new Prime Minister of the United Kingdom. He will be great!"
He added later at a speech that "they call him Britain Trump" and that Brexit Party leader Nigel Farage is "going to work well with Boris".
Mr Trump's daughter and White House adviser, Ivanka, initially congratulated Mr Johnson on becoming the next prime minister of "United Kingston", before correcting her mistake on Twitter.
Labour leader Jeremy Corbyn claimed Mr Johnson had yet to win the support of the country at large.
He tweeted: "Boris Johnson has won the support of fewer than 100,000 unrepresentative Conservative Party members by promising tax cuts for the richest, presenting himself as the bankers' friend, and pushing for a damaging No Deal Brexit.
"But he hasn't won the support of our country."
Mr Corbyn refused to clarify when he planned to launch a bid to topple Mr Johnson by calling a no confidence vote in parliament, only vowing to do it "when appropriate to do so".
Brexit Party leader Nigel Farage told Sky News "I just don't see how" Mr Johnson could deliver Brexit on 31 October without an early election because "hes' leading a party that's bitterly divided".
He added there had been no "formal" talks with Team Johnson but when pushed on if there had been informal conversations, said: "No - the fact people bump into each other in the same restaurant is not the same as discussions."
In the Tory leadership ballot, Mr Johnson won a total of 92,153 votes (66%) and Mr Hunt won 46,656 votes (34%).
The result follows a more than a month-long campaign in which both candidates travelled to all regions of the UK in their bid to win the support of the Tories' grassroots in a series of hustings events.
Mr Johnson vowed to take the UK out of the EU on 31 October "do or die", while Mr Hunt claimed his background as an "entrepreneur" made him the best candidate to negotiate Brexit.
In the earlier stages of the contest, during a series of votes among Tory MPs to whittle down a long list of candidates to a final two, Mr Johnson eventually secured the backing of more than half of his Conservative colleagues in parliament.
He won the support of 160 Tory MPs, with Mr Hunt backed by 77 Tory MPs.
But, despite his majority support among both Conservative members and MPs, Mr Johnson is unlikely to face a gentle first few weeks in Number 10.
A taste of the battles that will come in his aim of uniting the Tories was delivered on Monday by Sir Alan Duncan, who quit as a foreign office minister.
Sir Alan resigned from government in order to launch an - ultimately unsuccessful - attempt to force Mr Johnson to face a vote of confidence in his leadership even before becoming prime minister.
Mr Johnson's refusal to rule out a no-deal Brexit will also likely bring him headaches, with the government he takes over having a working majority of just two.
It means only a small group of Tory rebels would be needed derail Mr Johnson's Brexit strategy in the House of Commons - partly explaining why the incoming prime minister has not dismissed the possibility he could suspend parliament to push through a no-deal Brexit.
Chancellor Philip Hammond is set to lead a series of current cabinet ministers out of government prior to Mr Johnson's entry into Number 10, due to their opposition to leaving the EU without a withdrawal deal.
Mr Johnson is reported, by The Times, to have held secret meetings with Mr Hammond, Justice Secretary David Gauke and International Development Secretary Rory Stewart amid concerns they prove to be a "nightmare" on the back benches after leaving government this week.
After holding her last cabinet today, Mrs May will tomorrow make her last Commons appearance as head of the government.
She will take Prime Minister's Questions for a final time on Wednesday before then heading to Buckingham Palace to formally resign to the Queen and recommend her successor.
Mr Johnson will then make his own trip to Buckingham Palace to be invited to form a new government, before likely making a statement in Downing Street before stepping into Number 10.