France’s four main leftwing parties have agreed to form a “New Popular Front” (NPF) to contest the snap election, as the far-right leader Marine Le Pen said she would seek a “national unity government” if her National Rally (RN) wins, Ednews reports via The Guardian.

The Socialist party (PS), Greens, Communists and France Unbowed (LFI), led by the hard-left firebrand Jean-Luc Mélenchon, will campaign on a common platform and field a single joint candidate in each of the 577 parliamentary constituencies.

“A new page in the history of France has been written,” they said in a joint statement. Mélenchon tweeted his “warmest congratulations and thanks to our negotiators who had four sleepless nights” deciding on the programme and 577 candidates.

Macron called the snap ballot last Sunday after his list in the European elections suffered a crushing defeat at the hands of the RN, managing less than half the far-right party’s score. The vote will be held over two rounds on 30 June and 7 July.

The LFI MP François Ruffin said the left could now “start our campaign – with the aim of winning!”. Raphaël Glucksmann, who led a successful Socialist-backed list in the European elections, said he would also back the alliance.

“We can’t leave France to the Le Pen family,” Glucksmann told France Inter radio, adding that the NPF looked like the only way to prevent a far-right victory in the election, France’s most momentous in decades.

Glucksmann, whose list scored about 14% in the EU elections, just behind Macron’s camp, accused the president of “plunging France into chaos” and “opening the way to power for the far right”.

It was unclear who would lead the NPF and be its candidate for the post of prime minister. Glucksmann ruled out the bombastic and divisive Mélenchon, saying: “We need someone who can achieve consensus.”

Manuel Bompard, a senior LFI MP, said the alliance’s aim would be to “offer the country a complete break with the policies of Emmanuel Macron, so as to respond to the people’s most immediate needs, and to implement the necessary green transition”.

The NPF, presenting its policies on Friday, said its top priority if elected would be the cost of living crisis, which was “harming the lives and confidence of the French people”. It pledged to cap the price of essential foods, as well as electricity, gas and petrol.

The parties also said they would immediately reverse the unpopular pension changes pushed through last year by Macron’s government and return the French retirement age to 60, as well as overturning a more recent change to unemployment benefits and introducing a wealth tax.

They said France’s minimum wage and pension would be raised, while the NPF would also demand an immediate ceasefire in Gaza, recognise the state of Palestine, continue supplying necessary arms to Ukraine and legislate for carbon neutrality by 2050.