His resignation after just 27 days left Lecornu with the unwanted record of the shortest time in office of any prime minister since France's Fifth Republic was set up in 1958.

Still just 39, Lecornu had been one of the few faces of continuity in the French cabinet at a time of multiple changes of government, serving for more than three years as defence minister before Macron named him premier on September 9.

From day one, he faced an uphill struggle to survive. Both his predecessors were ousted by a parliament where pro-Macron forces are in the minority after elections in 2024 left the chamber deadlocked.

During just over three weeks in office, the French public barely heard him speak while he granted few interviews. He broke records with the length of time it took him to name his cabinet, with the line-up only announced Sunday evening.

But the hours of closed-door talks and discretion came to nought on Monday when Lecornu threw in the towel after his cabinet nominations infuriated the right.

"The conditions were not fulfilled for me to carry out my function as prime minister," Lecornu said.

In a swipe at the right, he denounced "partisan appetites" and added: "One must always put country before party".

His low profile and penchant for working behind the scenes caused irritation among some, although there was acknowledgement that he held the poorest of hands with a minority government facing hostility from the left and right.

"He is the Paganini of negotiation," said a high-ranking figure in the pro-Macron forces referring, to the 19th-century Italian virtuoso.

"But his violin has no more strings."

- Not 'presidentiable' -

The ultimate Macron loyalist, Lecornu had held his job as defence minister throughout almost all Russia's invasion of Ukraine, successfully expanding the defence budget, while carefully remaining in the shadows with infrequent media appearances.

One of his key assets for Macron was that he is not what is known in France as "presidentiable", namely someone who harbours ambitions of winning the Elysee Palace for themselves.

Lecornu is "a loyal soldier who doesn't have too much charisma or presidential potential", one ministerial adviser told AFP on condition of anonymity.

A career politician, Lecornu started out as a parliamentary assistant aged just 19. He had held ministerial posts ever since Macron came to power in 2017 and was promoted to defence minister in May 2022.

Interested in politics from an early age, Lecornu's career set records for hitting milestones at an early age, initially with the conservative UMP party of former president Nicolas Sarkozy.

He became France's youngest-ever ministerial adviser in 2008, joining Bruno Le Maire -- later Macron's long-serving finance minister -- on the Europe brief.

Ironically, the appointment of his former mentor Le Maire as defence minister sparked the wave of anger from the right that precipitated his downfall, with "BLM" seen as the incarnation of Macron's budgetary policies.

A graduate in public law rather than the elite administration or business institutions that traditionally shape top French leaders, Lecornu has made sure to keep up his local roots.

In 2015, he was the youngest-ever president of a French department, Eure in Normandy, after serving as mayor of his hometown Vernon.

He reached ministerial rank at 31, covering portfolios including the environment and overseas territories before landing at defence.

On taking office as premier, he promised "breaks" with the past and to be "more creative", vows he appeared unable to keep.

But even his opponents applauded the manner in which he had given way, with Socialist leader Olivier Faure saying he had resigned with "dignity and honour".