Nicknamed "Mr Deconfinement” – the term used for France’s gradual exit from coronavirus lockdown – Castex is the first member to be named in a new team that will steer the next phase of Macron’s five-year mandate.
A statement from the Elysée Palace said the 54-year-old career public servant had been asked to form a government.
"He is an all-rounded and versatile senior official who will be keen to reform the state and carry out a peaceful dialogue with the territories," the Elysee added.
Who is Jean Castex?
Mayor of the Pyrenean town Prades, Castex is a member of the right-wing Les Républicains party who has worked with multiple governments.
When he was given the delicate task of handling the government's lockdown exit plan back in April, Philippe said Castex was "formidable in his efficiency".
A one-time advisor to former president Nicolas Sarkozy, Castex is little known to the public but has been widely praised for his interpersonal skills within political circles. He has never before held the post of a minister.
Ministerial shake-up
France's full ministerial reshuffle – expected by Wednesday – is seen as an attempt to bolster Macron’s environmental credentials after his La République en Marche (LReM) party was battered in municipal elections last Sunday.
The ruling party lost all major cities to the greens, leaving the president without a local power base ahead of his re-election bid in 2022.
In an interview with regional media Thursday, Macron said the government would be injected with “new talent” and “personalities from different backgrounds” as he charted a new course for the last two years of his term.
He described his relationship with Philippe as “historic”, saying the former prime minister – who is not a member of LReM – had done a “remarkable job” as head of the government.
“For three years by my side he has done a remarkable job with successive governments and we have carried out some important reforms ... we have a relationship of trust,” Macron said.
