French President Emmanuel Macron has accepted his resignation, the Elysee Palace said.
Mr Lecornu’s resignation comes just 14 hours after he appointed his cabinet – and after political rivals threatened to topple his government.
He announced on Sunday that he had appointed his ministers, with the new cabinet set to hold its first meeting on Monday afternoon.
But the line-up had angered political allies and opponents alike, who either criticised that it was too right-wing or not right-wing enough, raising questions over how long it could last in a fragmented parliament where no party holds a majority.
Mr Lecornu, 39, an ally to Mr Macron, was the seventh prime minister appointed by the president – and the fifth in just two years.
His sudden resignation on Monday morning was unexpected and unprecedented, and resulted in more turmoil amid France’s political crisis.
Since Mr Macron was re-elected in 2022, the parliament has been unstable, and the president’s decision to call a snap election last year further deepened the crisis by producing an even more fragmented parliament.
After Mr Lecornu resigned, Jean-Luc Melenchon, the leader of far-left France Unbowed, said his party was calling for Mr Macron to be impeached, while the far-right National Rally immediately urged Mr Macron to call another snap election.
“There can be no return to stability without a return to the polls and the dissolution of the national assembly,” National Rally leader Jordan Bardella said.
Mr Lecornu’s resignation also resulted in French stocks and the euro dropping sharply.
French banks were leading a financial market sell-off, with the Societe Generale down by more than 6% on the CAC 40 in the moments after the announcement, while BNP Paribas and Credit Agricole were also sharply lower.
The index was 1.5% in the red.
The euro also fell back against sterling and the dollar, while French government borrowing costs, reflected on bond markets, hit levels last seen almost a month ago when the country was back in the same political stalemate.
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