French Prime Minister Elisabeth Borne resigned from government on Monday before President Emmanuel Macron unveiled a Cabinet reshuffle to try for new momentum in the final three years of his presidency.
Education Minister Gabriel Attal, 34, was emerging as the favourite to succeed Ms Borne after days of intense, closed-door manoeuvring.
If Mr Attal is appointed, he would become France's youngest ever and first openly gay prime minister.
"Ms Elisabeth Borne today submitted the resignation of the government to the President, who accepted it," the Elysee Palace said in a statement.
It said that she and other ministers would continue to handle daily business until a new government is formed.
But Ms Borne's resignation letter to Mr Macron, a copy of which was seen by AFP, hinted that she would have preferred to stay in her job.
"While I must present the resignation of my government, I wanted to tell you how passionate I was about this mission," she wrote.
While some expected a new prime minister to be quickly named during the evening, a source close to Mr Macron said the announcement would come on Tuesday morning.
It was not immediately clear if this was deliberately slow or due to last-minute objections from government figures over the possible naming of Mr Attal.
Commentators consider the reshuffle to be essential in relaunching Mr Macron's centrist presidency for its last three years and prevent him becoming a "lame duck" leader after a series of crises.
Since he beat the far right to win a second term in 2022, he has faced protests over unpopular pension reforms, the loss of his majority in parliamentary elections and controversy over immigration legislation.
Ms Borne, 62, the second woman to lead the French government, has weathered these problems but never dispelled doubts about her future.
Writing on X, Mr Macron thanked her for "work in the service of our nation that has been exemplary every day".
Other possible candidates to succeed Ms Borne include Defence Minister Sebastien Lecornu, 37, and Julien Denormandie, 43, a former agriculture minister.
But a source close to the government said that Mr Attal was now the favourite to succeed Borne.
Under the French system, the president sets general policies and the prime minister is responsible for day-to-day government management, meaning the latter often pays the price when an administration runs into turbulence.
While Mr Macron cannot run again in 2027 presidential elections, relaunching his government is considered to be crucial to help prevent far-right figurehead Marine Le Pen becoming president.
European Parliament elections in June will also pose a major test, with Mr Macron's Renaissance party risking embarrassment at the hands of Ms Le Pen's National Rally (RN).
Despite his age, Mr Attal is a more political figure than the technocratic Ms Borne, and polls have shown him to be one of the most popular government ministers.
If named, he would go toe-to-toe ahead of the European elections with another rising star of French politics, the even younger Jordan Bardella, 28, who is now party leader of the far-right RN.
Other key posts are also subject to uncertainty in particular that of Interior Minister Gerald Darmanin, 41, a right-winger who led the immigration reform but burnt his fingers when it was initially rejected by Parliament.
The futures of Foreign Minister Catherine Colonna and long-serving Finance Minister Bruno Le Maire were also uncertain.
Mr Macron likes "keeping all options open until the last moment", a source close to the Elysee said.
The new premier will be the fourth prime minister since 2017 under Mr Macron, who is accused by critics of micro-managing and centralising power in the Elysee.
"I have a scoop for you. I know the name of the prime minister," left-wing politician Raphael Glucksmann joked on France 2 television.
"It's Emmanuel Macron! And the foreign minister will also be Emmanuel Macron, as will the defence minister and the culture minister."
