It came amid a record abstention rate of 59% across the country.
A green wave swept over France on Sunday as the environmentalist party and its left-wing allies won control of a clutch of major cities including Lyon, Strasbourg and Bordeaux.
The centrist party of President Emmanuel Macron, La Republique En Marche (LREM), however, failed to capture any major cities, prompting talks of a governmental reshuffle.
In Paris socialist mayor Anne Hidalgo — endorsed by the greens — was re-elected with 48.7% of the vote.
The far-right Rassemblement National (formerly Front National), meanwhile, won in Perpignan. It is the first time it will be at the helm of a city of more than 100,000 inhabitants.
But while the Europe Ecology-The Greens (EELV) party toasted their unprecedented triumph, it came amid a record abstention rate of 59% across the country.
'A giant step'
EELV described the results a "historic".
"Today, ecology is taking a big step. A giant step," the party's secretary Julien Dayou said in a statement, adding that "it is THE mandate to act for climate and social justice."
"The French are ready for change. Great, so are we," he went on.
In Marseille, France's second city, the list led by the Greens has won the most seats in the local council but the mayorship is not yet assured as they don't have a majority. They will need the backing of smaller formations. A vote will be held later in the week.
The party, which formed alliances with mostly left-wing formations including La France Insoumise, the Communists and the Socialists, also won a clutch of second-tier cities including Grenoble, Poitiers, Annecy, and Tours.
The alliances they formed will also see them play key roles in other local councils across the country, including in Montpellier but also in Paris.
The capital was easily secured for another six-year term by Hidalgo, providing the Socialist party with its first spot of respite since 2017 when it was all but wiped out in presidential and parliamentary elections. It also came in sixth place in last year's European ballot.
But Sunday's poll showed the party retains a strong local anchoring — Socialist mayors held onto cities such as Lille, Nantes, Brest, and Rennes.
LREM 'taking root'
Its poor local implantation may have been one of the reasons LREM was routed in these elections. The centrist party, formed by Macron in 2016, did not win any of the big cities it hoped to secure and gathered just over 13% of the votes in Paris.
The party's campaigning has also been beset by infighting. In the capital, LREM's chosen candidate, Benjamin Griveaux, withdrew following a sex scandal but the LREM vote was split after Cedric Villani rebelled against the party to run.
In Lyon, LREM initially endorsed Gerard Collomb, a former close ally of Macron who ran France's third most populous city for 17 years, but withdrew its backing in May over his decision to form an alliance with the right-wing Les Republicans party.
Commenting on the results, Stanislas Guerini, LREM's general secretary, argued that the party had taken "its first step towards local establishment."
"We would, of course, have preferred to move the lines more but a new generation of local elected representatives is taking root. From this generation will future LREM mayors be born," he added.
The only bright spot for the ruling party was the re-election of Prime Minister Edouard Philippe in the northern city of Le Havre where he won with almost 59% of the votes against the Communist Party deputy Jean-Paul Lecoq.
A majority of French people are now keen for a government reshuffle, according to an IPSOS poll, although most respondents declared themselves in favour of a "limited" one.