LONDON (AP) — British Prime Minister Keir Starmer said Monday he will resign, forced out by his own party after missteps and mistakes soured voters' goodwill following a landslide election victory two years ago on a promise of steady leadership and economic growth.

Starmer says he will remain caretaker prime minister until his Labour Party chooses a new leader — with expectations growing that it will be former Greater Manchester Mayor Andy Burnham.

Burnham confirmed on social media that "I will put myself forward as part of this process." Former Health Secretary Wes Streeting, who was considered his main rival for the top job, said he will back Burnham.

It was Burnham's victory in a special parliamentary election last week that triggered Starmer's decision to resign, as Labour lawmakers flocked to the charismatic former mayor in the hope he can revive the party's fortunes. After nearly a decade as mayor of the northwestern city, Burnham returned Monday to Parliament, where he took the oath of office in the House of Commons.

Only members of Parliament are eligible for the party leadership.

READ MORE: How UK's Keir Starmer went from election landslide to downfall

Streeting's statement makes it more likely that Burnham will be selected without a leadership contest.

Britain's next election does not have to be held until 2029. Asked if he would call an early vote if he becomes prime minister, Burnham said: "You're jumping several hurdles ahead there."

Starmer is the sixth prime minister in a decade to stand outside No. 10 Downing St., and announce a premature departure. His statement came the day before Britain marks the 10th anniversary of its vote to leave the European Union, a decision that still roils the country's economy and politics.

After weeks of insisting he would fight to keep his job, Starmer conceded to growing pressure to hand over to a new leader who can try and revive the government's flagging fortunes. He led Labour to a landslide election victory in July 2024, but since then his popularity and that of the party have plummeted.

A new leader in place within weeks

Starmer made the announcement outside his official residence, where he delivered his first speech as prime minister two years ago. His voice choked with emotion near the end of the brief statement, which was watched by his staff, Cabinet ministers and scores of journalists.

"The question my party is asking now is whether I am best placed to lead us into the next general election," Starmer said. "I have heard the answer of my parliamentary party to that question, and I accept that answer with good grace."

He said he spoke to King Charles III, Britain's constitutional monarch, to inform him of the decision.

Starmer spent the weekend pondering his future following Burnham's special election victory.

Starmer said nominations for a leadership contest will open July 9, and the new leader will be in place by the time Parliament returns from its summer break on Sept. 1.

If Burnham is the only candidate, the change could come by mid-July.

Starmer struggled to fulfill election pledges

Starmer has struggled to deliver promised economic growth, repair tattered public services and ease the cost of living. He has been hamstrung by repeated missteps, including his decision to appoint Peter Mandelson, a scandal-tarnished friend of Jeffrey Epstein, as U.K. ambassador to the United States.

Labour is losing liberal voters to the growing Green Party and facing a rising Reform UK, the Nigel Farage -led anti-immigration party that consistently leads in nationwide opinion polls.

U.S. President Donald Trump weighed in even before an announcement, linking Starmer's exit to two of the Republican leader's recurring grievances: immigration and renewable energy.

"Keir Starmer will resign as Prime Minister of The United Kingdom. He failed badly on two very important subjects- IMMIGRATION AND ENERGY (OPEN NORTH SEA OIL!). I wish him well! President DJT," Trump posted on his social media platform.

Starmer's initially warm relationship with Trump has soured in recent months over issues including the Iran war, which the U.K. didn't join.

Praised on the world stage

In contrast to missteps domestically, Starmer has won praise for his international role, notably in rallying European support for Ukraine in its fight against Russia's invasion, and working to mitigate the economic and political turmoil unleashed by the Iran conflict.

A NATO summit in Turkey next month may be his last foray on the world stage as Britain's leader.

Ukrainian President Volodymyr Zelenskyy, posting on X, thanked Starmer for his support and cooperation "that have helped make our Europe and our protection of life stronger."

European Commission President Ursula von der Leyen praised Starmer's legacy.

"It can take many leaders years to grow into the statesman you became in just two years," she said on X. "European and Ukrainian security is stronger because of you. Thank you, dear Keir."

While many Labour lawmakers have rallied behind Burnham, some have said that Starmer had been treated unfairly. London legislator Neil Coyle railed on X against "the prospect of an utter stitch-up & the media circus being rewarded."

Many hope Burnham can connect with voters

Burnham is the front-runner to succeed Starmer because many people see him as the best person to defeat the anti-immigration Reform Party at the next election, said Olivia O'Sullivan, an analyst at London's Chatham House think tank.

Burnham appeals to Labour Party lawmakers who were frustrated by the way Starmer has governed, O'Sullivan said. Many hope that he will set out a "clearer vision" and connect with voters in parts of the country that are in danger of turning to Reform.

Still, O'Sullivan cautioned that may not translate into genuine change.

"It's absolutely correct that that is not the same thing as offering a radically different set of policies or even a particularly clear policy program," she said.

Associated Press writers Danica Kirka in London and Sam McNeil in Brussels contributed.