Brexit hardliner Boris Johnson won the contest to lead Britain's governing Conservative Party and will become the country's next prime minister, tasked with fulfilling his promise to lead the UK out of the European Union "come what may."
He defeated his rival Jeremy Hunt overwhelmingly in a vote of Conservative Party members.
He will be installed as prime minister in a formal handover from Theresa May on Wednesday.
The victory is a triumph for 55-year-old Johnson, an ambitious but erratic politician whose political career has veered between periods in high office and spells on the sidelines.
Johnson has vowed that Britain will quit the European Union on the scheduled date of October 31 even if it means leaving without a divorce deal.
But he faces a rocky ride from a Parliament determined to prevent him from taking the UK out of the 28-nation bloc without a withdrawal agreement.
Several Conservative ministers have already announced they will resign to fight any push for a "no-deal" Brexit, an outcome economists warn would disrupt trade and plunge the UK into recession.
Fears that Britain is inching closer to a "no-deal" Brexit weighed on the pound once again Tuesday. Before the announcement, the currency was down another 0.3 percent at $1.2441 and near two-year lows.
May stepped down after Britain's Parliament repeatedly rejected the withdrawal agreement she struck with the 28-nation bloc. Johnson insists he can get the EU to renegotiate — something the bloc insists it will not do.
If not, he says Britain must leave the EU on Halloween, "do or die."