Sunak had announced his candidacy Sunday to become the next prime minister of the United Kingdom in a bid to “turn around” the country’s economy and “unite” the Conservative party.

Sunak will succeed Liz Truss seven weeks after she defeated him in the previous Tory contest. The ex-chancellor gained the support of well over half of Tory MPs, with Mordaunt struggling to reach the threshold of 100 MPs to get on the ballot.

He will become the UK's first British Asian premier and at 42, the youngest in more than a century.

Meanwhile, Labour have reiterated their call for a general election, as have the Scottish National Party and the Liberal Democrats.

Meanwhile, Mordaunt walked into the 1922 committee of backbench MPs, which Sunak is about to address, saying she is “good” and “going to support the new PM.”

She entered the room to a rapturous banging of fists on desks — which in Tory MP tradition is a round of applause.

Sir Graham Brady, chairman of the 1922 Committee, confirmed Rishi Sunak would be the next leader of the Conservative Party, and the next prime minister.

Sunak was the only candidate after Mordaunt pulled out just ahead of the 14:00 deadline for nominations.

Mordaunt’s statement following her withdrawal read: "Our Party is our membership. Whether we are elected representatives, activists, fundraisers or supporters. We all have a stake in who our leader is.

"These are unprecedented times. Despite the compressed timetable for the leadership contest it is clear that colleagues feel we need certainty today. They have taken this decision in good faith for the good of the country.

"Members should know that this proposition has been fairly and thoroughly tested by the agreed 1922 process.

"As a result, we have now chosen our next prime minister. This decision is an historic one and shows, once again, the diversity and talent of our party. Rishi has my full support.

"I am proud of the campaign we ran and grateful to all those, across all sides of our party, who gave me their backing. We all owe it to the country, to each other and to Rishi to unite and work together for the good of the nation. There is much work to be done."

Reacting to the news that Sunak will be the UK's next prime minister, Foreign Secretary James Cleverly told the BBC it's a "very positive move".

Cleverly — who had originally backed former prime minister Boris Johnson to be leader again Sunday, before swapping to Sunak after Johnson pulled out — said Sunak is the most experienced candidate to lead the country, adding that he's a "smart and talented guy".

He said after the "difficult" and "brutal" last few months, the government can now focus on the British people, delivering good governance, and supporting the UK's international friends, such as Ukraine.

They "should be the only things that we think about," he said. Another week's delay to the Tory leadership contest would have been "counterproductive", he added.

Scottish Conservatives leader Douglas Ross too congratulated Sunak on becoming the new Conservative party leader and prime minister, stating that he is "uniquely well equipped for the task".

Ross said: "Our country — like others around the world — faces tough economic challenges.

"Against that backdrop, it's important that we have someone at the helm with a proven track record in running the nation's finances, who can provide economic stability and reassurance to the markets."

He said recent weeks had been "difficult and unsettling" for the party and the country, and that all the focus must now be on "bringing the nation together and navigating through the tough economic conditions we face."

Labour's deputy leader Angela Rayner said Sunak will become the UK's next prime minister without him "saying a word" about what he plans to do in No 10.

Reiterating Labour's call for a general election, Rayner added, Sunak is "already putting party before country" in holding a closed-door address to Tory MPs this afternoon.

Meanwhile, Lib Dem leader Sir Ed Davey said the Tories are installing "another out-of-touch prime minister".

In a statement, Davey said the Conservative Party has "trashed the British economy", and repeated his call for a general election.

He said: "Now Conservative MPs have installed another out-of-touch prime minister with no plan to repair the damage and without giving the British people a say."

Davey added that Sunak has shown he "doesn't understand the challenges facing struggling families and pensioners".

He predicted "more of the same, as Conservative MPs plot and squabble amongst themselves while completely ignoring the huge challenges facing the country".

"The only way to end the chaos is a general election now," he said.

The pound and British government bond prices rose slightly on news of Mordaunt's withdrawal — and therefore confirmation Sunak would be the next prime minister. Against the dollar, the pound rose slightly by 0.15%.