President Emmanuel Macron has named the European Union's former Brexit negotiator Michel Barnier as France's new prime minister, tasking him with forming a new government.

A statement from Mr Macron's office was released on Thursday, announcing 73-year-old Mr Barnier's appointment.

In the statement it said Mr Barnier had been tasked "with forming a unifying government to serve the country and the French people".

"This appointment comes after an unprecedented cycle of consultations during which, in accordance with his constitutional duty, the president ensured that the prime minister and the future government would meet the conditions to be as stable as possible and give themselves the chances of uniting as broadly as possible," the statement said.

The move came after a snap election in June which left France with a hung parliament and 50 days of caretaker government while major parties agreed on a new prime minister.

Barnier and Macron in Paris

French President Emmanuel Macron (right) has nominated Michel Barnier (left) for prime minister. (AP: Michel Euler)

National Rally politician Sebastien Chenu told BFM TV that the far-right party would wait to see what Mr Barnier has to say on immigration, and on changing France's voting system, before condoning or condemning Mr Macron's choice.

The left-leaning New Popular Front on their own won't have enough votes to vote Mr Barnier down, but could call street protests.

Far-left leader Jean-Luc Melenchon predicted the new prime minister would not get a majority backing in the bitterly divided National Assembly.

Mr Barnier replaces Gabriel Attal, who resigned on July 16 but stayed on with his ministers in a caretaker capacity during the 50 days France was left without an official prime minister.

The caretaker government was responsible for handling the Paris Olympics.

Mr Macron slams the door on a potential leftist government, leaving a potential hung parliament with no prime minister.

Originally from France’s Alpine region of Haute-Savoie, Mr Barnier rose to become the EU's chief negotiator in the difficult talks with Britain over its Brexit departure from the bloc.

He has also served as the French foreign, European affairs, environment and agriculture minister — and twice as a European commissioner — but until now had never had a tilt at any leadership post, like that of president or prime minister.

At 73, Mr Barnier will be the oldest prime minister in France's modern political history. Mr Attal was the youngest.

Mr Barnier will have the daunting challenge of trying to push reforms and the 2025 budget at a time when France is under pressure from the European Commission and bond markets to reduce its deficit.