Rishi Sunak has been installed as Britain's third prime minister of the year by King Charles III.
He will appoint a Cabinet that will have to wrestle with the UK's economic and political crises.
Sunak, the UK's first leader of color, was selected as leader of the governing Conservative Party on Monday as it tries to stabilize the economy, and its own plunging popularity, after the brief, disastrous term of Liz Truss.
Truss will depart after making a brief public statement outside 10 Downing St., seven weeks to the day after she was appointed prime minister by Queen Elizabeth II. The queen died two days later. Now her son will take over the ceremonial role of accepting Truss' resignation at Buckingham Palace before asking Sunak to form a government.
Sunak - at 42 the youngest British leader for more than 200 years - must try to shore up an economy sliding toward recession and reeling after his predecessor's experiment in libertarian economics, while also attempting to unite a demoralized and divided party that trails far behind the opposition in opinion polls.
His top priorities will be appointing Cabinet ministers, and preparing a budget statement that will set out how the government plans to come up with billions of pounds (dollars) to fill a fiscal hole created by soaring inflation and a sluggish economy, and exacerbated by Truss' destabilizing economic experiments.
The statement, set to feature tax increases and spending cuts, is currently due to be made in Parliament on Monday by Treasury chief Jeremy Hunt - if Sunak keeps him in the job.
Sunak, who was Treasury chief himself for two years until July, said Monday that Britain faces "a profound economic challenge."
Sunak becomes prime minister in a remarkable reversal of fortune just weeks after he lost to Truss in a Conservative election to replace former Prime Minister Boris Johnson. Party members in the summer chose her tax-cutting boosterism over his warnings that inflation must be tamed.
Truss conceded last week that she could not deliver on her plans - but only after her attempts triggered market chaos and worsened inflation at a time when millions of Britons were already struggling with soaring borrowing costs and rising energy and food prices.
The party is now desperate for someone to right the ship after months of chaos under Truss and Johnson, who quit in July after becoming mired in ethics scandals.
Sunak was chosen as Conservative leader after becoming the only candidate to clear the hurdle of 100 nominations from fellow lawmakers to run in the party election.
Sunak defeated rival Penny Mordaunt, who may get a job in his government, and the ousted Johnson, who dashed back from a Caribbean vacation to rally support for a comeback bid but failed to get enough backing to run.
As well as stabilizing the UK economy, Sunak must try to unite a governing party that has descended into acrimony as its poll ratings have plunged.
Conservative lawmaker Victoria Atkins, a Sunak ally, said the party would "settle down" under Sunak.
"We all understand that we've now really got to get behind Rishi - and, in fairness, that's exactly what the party has done," she told radio station LBC.
