Humiliated Rishi Sunak will attend the COP27 climate summit on Monday after a last-minute U-turn.
The Tory leader will fly to the talks in Egypt in a private government jet, joining world leaders including US President Joe Biden.
Mr Sunak had pulled out of the summit due to “pressing domestic commitments” - including the November 17 Autumn Statement.
But after a Tory backlash and his rival Boris Johnson vowing to go, he tweeted: "I will attend COP27 next week: to deliver on Glasgow's legacy of building a secure and sustainable future."
He added: "There is no long-term prosperity without action on climate change. There is no energy security without investing in renewables."
Downing Street claimed he changed his mind after making "good progress" on the Autumn Statement.
But it came after public interventions from COP26 President Alok Sharma, Climate Change Committee chairman Lord Deben and ex-Chancellor George Osborne.
Labour's deputy leader Angela Rayner said he had been "dragged kicking and screaming into doing the right thing."
Labour leader Keir Starmer added: “Caving in to criticism is not leadership. Real leadership is seizing your seat at the table.”
Scores of world leaders are planning to speak in the opening days of the two-week summit, which kicks off on Sunday.
No10 said: "Following discussions with the Chancellor this week, he has now agreed to attend. The PM feels there is sufficient space to make this trip."
Mr Sharma, who presided over Cop26 in Glasgow last year, praised Mr Sunak's reversal. But Shadow climate secretary Ed Miliband said: "The guy is a phoney."
He added: "The Prime Minister has been shamed into going to COP27 by the torrent of disbelief that he would fail to turn up.
“Yet again we see a Prime Minister who only makes decisions for reasons of political management not the national interest."
Friends of the Earth international climate campaigner Rachel Kennerley welcomed Mr Sunak having "seen sense and decided to attend" and urged him to "rebuild" the UK's climate reputation.
Mr Sunak will hope to make progress on the commitment to halt deforestation by 2030 and to agree new partnerships on clean and renewable energy, Downing Street said.
Mr Sunak's spokesman said he would not "pre-empt" conversations when asked if he will raise the imprisonment of British-Egyptian pro-democracy activist Alaa Abdel-Fattah, who is on hunger strike.
"We are working hard to secure Alaa Abdel-Fattah's release. We are raising his case at the highest levels of the Egyptian government," the spokesman said.
Amnesty International said Mr Sunak must tell Egyptian President Abdel Fattah El-Sisi the activist's "life now hangs in the balance".
Despite the U-turn, King Charles is still not planning to attend COP27 after being advised not to do so by No10.
A Buckingham Palace spokesman said there is "unanimous agreement" with the Government that it is not right for the environmental campaigner to attend.
