Britain's governing Conservative Party selected Boris Johnson - a strong supporter of the Brexit campaign - as its leader and he will serve as the country's next prime minister.
He was a strong favorite to get the job. Johnson formerly served as foreign secretary and mayor of London.
Johnson easily defeated rival Jeremy Hunt in the balloting of 160,000 Conservative members.
Johnson will replace Theresa May, who announced her resignation last month, and will officially become prime minister on Wednesday.
In a speech Tuesday, Johnson said he would "deliver Brexit, unite the country" and defeat the Labor opposition. He has vowed that Britain will leave the European Union on the scheduled date of Oct. 31, with or without a deal in place.
"It can be expected that there will be a knee-jerk reaction for the pound to the downside on the announcement that Boris Johnson has won the keys to Number 10," said Nigel Green, chief executive and founder of deVere Group. "But as it is expected and priced-in, it will not drop too much further or for too long."
Green added that "sterling is currently floundering due to the ongoing Brexit chaos and uncertainty which has put the brakes on the U.K. economy.
"The pound's weakness has also been driven by fears regarding Mr. Johnson's embrace of the possibility of a no-deal Brexit on 31 October, with many forecasting an economic shock for Britain if this were to occur."
"However, there's also an argument to suggest that Mr. Johnson's controversial 'do or die' approach - and a hard break - will at least end the years of failed negotiations which have fueled endless uncertainty for business and the markets," Green said.
The British pound slipped to $1.2447 vs. the dollar.
The FTSE 100 in London was rising 1% on Tuesday to 7,590.07.
Donald Trump tweeted Tuesday: "Congratulations to Boris Johnson on becoming the new Prime Minister of the United Kingdom. He will be great!"