Emmanuel Macron's policies if it wins historic polls that could propel the far right to major gains in parliament.
Far-right figurehead Marine Le Pen, also making a pitch to voters, pledged a «national unity government» if her party takes power in the snap legislative elections.
Macron on Sunday stunned France by calling polls after Le Pen's far-right National Rally (RN) scored more than double his centrist alliance's result in last week's European elections.
Left-wing outfits including hard-left France Unbowed (LFI), the Socialist, Communist and Green parties on Thursday agreed an election alliance called the New Popular Front.
On Friday, they unveiled a joint manifesto, whose headline measures included jettisoning Macron's controversial immigration and pension reforms if they win the polls to open on June 30, with a second round on July 7.
They also promised to «rise to the climate challenge» — without agreeing on whether to go ahead with modernising France's fleet of nuclear plants — and to keep up support for Ukraine against the Russian invasion.
«It's going to be either the far right, or us,» Greens party leader Marine Tondelier told reporters.
The coalition won backing from leading left-wing politician Raphael Glucksmann, 44, who led the Socialist-backed list in the European elections.
«We can't leave France to the Le Pen family,» he told broadcaster France Inter.
The name of the alliance is a nod to the Popular Front, a political alliance