France's left-of-center parties reached an alliance deal on Wednesday ahead of parliamentary elections in June, aiming for a strong showing to counter centrist President Emmanuel Macron.
In talks that dragged through the night, the Socialist Party (PS) fell in line alongside the Greens and the Communist Party (PCF) behind the hard-left La France Insoumise movement (LFI), which emerged as the dominant force on the left in April's presidential election.
"We want to elect MPs in a majority of constituencies to stop Emmanuel Macron from pursuing his unjust and brutal policies and beat the far-right," the PS and LFI said in a joint statement.
The alliance must still be approved by the Socialists' National Council on Thursday.
"No one on the left can win on their own," PCF leader Fabien Roussel told France Inter radio, saying the new alliance needed to harness "the immense hope among the French public, among workers, among young people who are asking us to unite."
LFI leader Jean-Luc Melenchon missed out on the April presidential runoff vote by a whisker, while the other left candidates were all but wiped out.
After Macron's win, Melenchon immediately called on voters to "elect him prime minister" and hand the left a National Assembly majority to block the president's reforms, including an unpopular plan to push the retirement age back from 62 to 65.
Like the presidential election, the legislative polls in France's 577 constituencies – which will be held this year on June 12-19 – work in a two-round system, meaning alliances offer the best chance of making it to the run-off.
The new allies have also agreed on Melenchon's core policy proposals, including raising the minimum wage, reducing the retirement age to 60 and rolling back labor market reforms introduced under former socialist president Francois Hollande.
(With input from AFP)