Macron named 73-year-old Barnier, a conservative and the European Union's former Brexit negotiator, as prime minister on Thursday, capping a two-month-long search following his ill-fated decision to call a legislative election that delivered a hung parliament divided in three blocs.
In his first interview as government chief, Barnier said on Friday night his government, which lacks a clear majority, would include conservatives, members of Macron's camp and he hoped, some from the left.
Barnier faces the daunting task of trying to drive reforms and the 2025 budget as France is under pressure from the European Commission and bond markets to reduce its deficit.
French Prime Minister Michel Barnier faces a potential no-confidence vote. (AP PHOTO)
The left, led by the far-left France Unbowed (LFI) party, has accused Macron of a denial of democracy and stealing the election after the president refused to pick the candidate of the New Popular Front (NFP) alliance that came top in the July vote.
Pollster Elabe published a survey on Friday showing 74 per cent of French people considered Macron had disregarded the results of the elections, with 55 per cent believing he had stolen them.
In response to the appointment of Barnier, whose centre-right Les Republicains party is only the fifth bloc in parliament with less than 50 MPs, left-wing party leaders, unions and student bodies called for mass protests on Saturday ahead of new action, including possible strikes on October 1.
France Unbowed said 130 protests would take place across the country.
Barnier was continuing consultations on Saturday as he looked to form a government, a tricky job given he faces a potential no-confidence vote, with an urgent draft budget for 2025 due to be discussed in parliament at the start of October.
NFP and the far-right National Rally together have a majority and could oust the prime minister through a no-confidence vote should they decide to collaborate.
The National Rally gave its tacit approval for Barnier, citing several conditions for it to not back a no-confidence vote - making it the de facto kingmaker for the new government.
"He is a prime minister under surveillance," National Rally party leader Jordan Bardella told BFM on Saturday.
"Nothing can be done without us."
