Lecornu, a close ally of Macron, took office as prime minister just four weeks ago but resigned on Monday amid government tensions, plunging France into a further political crisis.
But his return was confirmed on Friday after he was tasked by Macron with holding last-ditch talks with political opponents to find a path forward after months of instability in Paris.
Under the French constitution, a new budget for the coming year must be submitted to parliament by a prime minister by Monday.
"I have no other ambition than to get us out of this situation, which is objectively very difficult for everyone," Lecornu said in the Paris suburb of L'Haÿ-les-Roses on Saturday.
"So I give myself a pretty clear task," he said, referring to the budget deadline.
"And then either the political forces help me with it and we work together - or they don't."
"It is about how we ensure that on 31 December there is a budget for social security and a budget for the state."
Lecornu criticised the political deadlock that has gripped the country.
"What is ridiculous is the spectacle that the entire political world has been putting on for several days now," he said.
The prime minister urged political parties to overcome their differences to pass a budget by the end of the year, a crucial step in bringing France's widening fiscal deficit under control.
"It is about how we ensure that on 31 December there is a budget for social security and a budget for the state."
By Monday, Lecornu must present a draft budget bill - first to cabinet, and then on the same day to parliament.
That means, at a minimum, the ministers responsible for finance, budget and social security must be appointed by then.
France has been mired in political deadlock since a snap election in mid-2024, which left no camp with a majority.
While a left-wing alliance emerged with the most seats, Macron has steadfastly refused to work with the progressives, nominating a series of centrist and conservative prime ministers that have proven unable to build parliamentary majorities.
Lecornu has hinted that he could turn to the progressives as he faces the task of putting together a cabinet quickly over the weekend.
"I think we need a government that also reflects parliamentary reality. That is essential, that is democracy," he said.
The government is already facing a vote of no confidence from the opposition at the beginning of the week, which means that Lecornu and his future government team could be toppled as soon as Thursday.
with Reuters
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