Rishi Sunak was sworn in as the next Prime Minister of the United Kingdom on Tuesday, pledging to rectify the mistakes made by Liz Truss.

Mr. Sunak, aged 42, arrived in Downing Street following his appointment by King Charles III, who oversaw the first transfer of power.

In his first address as prime minister, he vowed to restore order despite what he termed a "grave economic catastrophe." The pound rose as markets reacted positively to his appointment.

He succeeds Ms. Truss only 49 days after she assumed power after an ill-conceived package of tax cuts fatally undermined her authority.

Ms. Truss "did not err in wanting to increase economic growth in this country. It is a worthy objective, and I respected her determination to effect change. But certain mistakes were made," Mr. Sunak remarked.

"I was elected as the head of my party and your prime minister in part to address these issues. This work commences today."

Mr. Sunak promised to reestablish trust as he drew a line under the premierships of Ms. Truss and Boris Johnson, who on Sunday abandoned an audacious comeback bid.

In a six-minute address in which he was not surrounded by family or supporters, he stated that ministers must make difficult decisions to reassure investors.

Mr. Sunak promptly reappointed Jeremy Hunt, the Chancellor of the Exchequer brought in to stabilize the economy.

As he began to construct his cabinet, ministers close to Ms. Truss, such as Simon Clarke and Jacob Rees-Mogg, announced their resignations.

"I am fully aware of how difficult things are. After all that has transpired, I am also aware that I must endeavor to reestablish trust, as Mr. Sunak explained.

"All I can say is I am not intimidated. I am aware of the high office I have accepted and aspire to meet its requirements."

The invitation to establish a government at Buckingham Palace was extended to Mr. Sunak after he won the Conservative Party leadership on Monday.

He is the youngest prime minister in more than 200 years, as well as the first of Hindu and Asian descent.

As Britain's third leader in two months, he faces a variety of obstacles, such as economic turmoil, soaring inflation, the war in Ukraine, and a fragmented ruling party.

Ukrainian President Volodymyr Zelenskyy was among the first foreign leaders to extend his greetings following US President Joe Biden's description of the event as a "milestone of historic significance."

France and the United Kingdom will "continue working to address the issues of the moment," including the war in Ukraine, according to French President Emmanuel Macron.

While opposition parties urge for an election, Mr. Sunak signaled that an early vote was unlikely by stating that he would revert to Tory platform vows in 2019.

About Mr. Johnson's victory that year, he stated, "I am sure he would agree that the mandate my party received in 2019 does not belong to a single person."

Mr. Johnson's resignation in July was precipitated by a cabinet mutiny when Mr. Sunak, the former chancellor of the exchequer, joined scores of colleagues in walking out.

But he termed Mr. Sunak's appointment a "historic day" and said it was an opportunity for the Conservatives to unite.

The president of the Southampton Hindu temple founded by Mr. Sunak's grandfather described Mr. Sunak's appointment as "our Barack Obama moment."

"It would unite the country, since he practises Hindu faith religiously and one of the fundamental beliefs we have is the whole globe is our family and we believe in unity in that respect," Sanjay Chandarana told PA.

As part of the handover's choreography, Mr. Sunak spoke outside the black door of 10 Downing Street and at a different lectern than Ms. Truss.

49 days after assuming office, Ms. Truss departed Downing Street with her husband and two daughters.

In a defiant goodbye address, she defended the pro-growth policies that contributed to her downfall, but she predicted that "better days are coming."

After her package of more than £40 billion ($45.2 billion) in tax cuts wreaked havoc on financial markets, Tory lawmakers turned on Ms. Truss.

However, she stated, "We simply cannot afford to be a low-growth nation in which the government's portion of our national income grows."

She felt honored to have presided through sorrow for Queen Elizabeth II, who nominated her as her penultimate prime minister two days before her death.