Mrs May stepped down after repeatedly failing to get Parliament to ratify her Brexit deal.
He told voters he would lead Britain out of the European Union by October 31, even if there is not a deal.
Prime Minister Theresa May will leave Downing Street after a three-year premiership that was mired by crises over Brexit.
Johnson later paid a visit to Pakistan in November 2016, when he met then-Prime Minister Nawaz Sharif, Pakistan Tehreek-e-Insaf (PTI) chairman and now Prime Minister Imran Khan, and Pakistan People's Party (PPP) chairman Bilawal Bhutto-Zardari, among others. They also fear big problems with worldwide trade.
The pound barely moved on Wednesday, with investors keen to see whether Johnson pushes ahead with a no-deal divorce.
It is a triumph for a man who has always wanted the top job, but Johnson, known for his jokes and bluster, is taking over at a time of huge political upheaval.
He derided "the doubters, the doomsters, the gloomsters" who believe the ebullient but chaotic Johnson can not succeed in breaking the Brexit impasse that defeated his predecessor, Theresa May.
Britain's governing Conservative Party is set to reveal who the name of the country's next prime minister, with Brexit champion Boris Johnson the strong favorite to get the job.
Hammond has condemned Johnson's willingness to accept a "no deal" exit as deeply irresponsible.
Open champion Shane Lowry: I sat in the vehicle park and cried
Neither of the final pair were ever under any pressure from the chasing pack as they dropped further back in the rough conditions. It's amusing , I sometimes struggle to play in front of the home crowd and have done in the past, but not over the last few days.
He was Mrs May's foreign secretary until resigning over Brexit.
Johnson has been the frontrunner in the race ever since a group of Tory MPs put their hat in the ring for the first phase of the leadership election within the Conservative parliamentary party.
A survey by the YouGov polling institute on Wednesday found his approval rating was just 31 percent. "We are once again going to believe in ourselves, and like some slumbering giant we are going to rise and ping off the guy ropes of self doubt and negativity".
A record number of ethnic minority politicians are expected to serve as ministers including Priti Patel, the former aid minister who resigned in 2017 over undisclosed meetings with Israeli officials, and employment minister Alok Sharma.
Brexit supporter Priti Patel, who May sacked as global aid minister for unauthorised contacts with the Israeli government, is also likely to get a top job.
Johnson defeated Hunt by 92,153 votes to 46,656 votes cast by members of the Conservative party. The UK is enmeshed with Iran in a naval dispute over the seizure of a tanker near Gibraltar, by the British, which was claimed to be breaching oil sanctions against Syria. US President Donald Trump tweeted.
Journalist and TV presenter Mehdi Hasan shared memories of Johnson as a younger man.
The outgoing PM - who is standing down after a revolt by Conservative MPs over her Brexit policy - congratulated her successor, promising him her "full support from the backbenches".
This comes as the Vice President of Sinn Fein, Michelle O'Neill, said, "Brexit will be catastrophic for this island", adding, "Boris Johnson needs to wake up from his fairy tale".
But Johnson-supporting Health Secretary Matt Hancock on Tuesday ruled out any form of electoral pact.