Borne previously served as Minister of the Environment, Transport and Labor.
He will lead a French government that is likely to be tasked with fulfilling President Macron’s campaign priorities: pension reform and increasing policies designed to combat climate change.
Borne was “charged with forming a government”, according to the Elysée.
She dedicated her nomination to “every little girl” during a ceremony that marked the transfer of power on Monday.
“Follow your dreams all the way,” Borne said in a speech. “Nothing must hold back the struggle for the place of women in society”.
Last Monday the Elysée announced that Castex had resigned.
The former mayor of his small hometown of Prades in southwestern France, Castex was a little-known figure when he became Prime Minister in July 2020. He went on to lead France’s response to the Covid-19 pandemic.