From Édith Piaf to Serge Gainsbourg, France is fiercely protective of the chanson tradition of character-driven French-language love songs. So it’s not often that someone is credited with reinventing the genre. Especially if that someone is a freeform-dancing, electro-influenced former care-worker hailing from the far-flung Atlantic coast.

In little more than a year, Zaho de Sagazan, a 24-year-old from the working-class shipyard town of Saint Nazaire, has gone from playing provincial music festivals to sweeping the board at les Victoires, the French Grammys. Her platinum album La Symphonie des Éclairs (“lightning symphony”) is seen as redefining 1950s and 1960s chanson française with its spiky lyrics about hypersensitivity, coercive control, cannabis, crushes and the climate crisis, all delivered in a deep, theatrically over-emphasised diction to rival Charles Aznavour. The emotion is compounded by the cold, thumping machine beats of French electronica she weaves into her songs.

“I like the idea of futuristic retro,” she says after opening the door to her parents’ house on a quiet street in Saint Nazaire. “I like the way chanson française can convey a universal emotion in so few words, but I’m also passionate about 70s, 80s, 90s synthesisers. I love Kraftwerk. Synthesisers can convey emotion too. And I thought: ‘I can’t be the only person who loves lyrics but also loves synthesisers and can very rarely find a song that has both.’”

Her live performances, with their incongruous crescendo from sedate piano ballads to sweaty electro dance sets, have been hailed by Libération as “the adrenalin that post-Covid France needed”. Two recent Paris dates sold out in three minutes and – in a rarity for a young musician who only sings in French – this autumn she’ll play a gig in London, then tour the US and Europe.

Saint Nazaire is central to her music: this working-class Atlantic port, one of the worst bombed French towns in the second world war, has shaped its mix of cold, hard electronic beats and quirky, flighty lyrics. “I was born into a very industrial world with lots of concrete,” she says. “This town was completely destroyed in the war and rebuilt with steel and concrete. Yet at the same time, it has this sweeping view out to the horizon. If Saint Nazaire is a mix of an industrial town and the poetry of the sea, my music is a little bit too.”

The fact that she has invited me to the bohemian ramshackle of her parents’ garden, where she curls up in a battered old armchair under a tree and cheerfully rolls a cigarette, reflects how far she places herself from the grandeur of the Paris star system. Her mother is a former literature teacher in a deprived area of the city. Her father, Olivier de Sagazan, is an artist, sculptor and performer who toiled for years before making it, and once stood barking like a dog for three hours in a square at Paris’s La Défense to warn of the dangers of the far right. She grew up in this “special house” of carefree creativity, as she calls it. She and her four sisters were allowed no TV but were all encouraged to have strong opinions and make a noise. “No one ever told us to be quiet,” she says.

When we speak, she is on a break from recording new electro tracks for a reissue of her album, not in a posh studio but on hired synthesisers in her parents’ backroom. It’s the same dark and chilly backroom where, aged 13, she taught herself to play piano on an out-of-tune upright. Her twin sister had blasted lovestruck piano ballads by the English singer Tom Odell from her bedroom speakers, and De Sagazan decided that howling with pain at the keyboard was good for processing emotions. “I was very, very sensitive and was in tears all the time,” she says. “I sat down at the piano to draw out this storm I had inside me.”

All this has made her studiously unconventional, which was in evidence when she was invited to open this year’s Cannes film festival by singing David Bowie’s Modern Love to the head of the jury, Greta Gerwig. Her deliberately absurdist, freeform-dancing take on it went viral after she wove through the audience of film stars, boldly kicked off her shoes and leapt about in socks on stage – moving in her personal style which she describes as “teenager dancing alone in their bedroom”.

“I felt I had to shake the festival up a bit,” she says. “The idea was to be a completely free woman who doesn’t care how she looks in the midst of this closed, self-conscious setting.” On the now famous socks, she shrugs: “I have a habit of taking my shoes off, I thought it would be more comfortable for dancing. I didn’t think it was a political act. But when you think it’s a festival which only a few years ago made women wear heels, well then yes, it can mean a lot of things. I hadn’t realised how much impact it would have. Some people said they cried watching it. There’s a thirst for liberty and authenticity right now.”

At the Paris Olympics closing ceremony, she was invited to sing a graceful choral version of the classic 1950s ode to Paris Sous le Ciel de Paris, made famous by Édith Piaf, in the Tuileries Gardens – but points out she would have been equally at home in the thumping French touch electro sessions that followed at the Stade de France.

Blending styles from different eras and places is a long tradition in modern French-language music – including by the acclaimed Belgian-Rwandan singer-songwriter/rapper, Stromae, whom De Sagazan cites as a key influence for his combination of “extraordinary lyrics and getting people dancing”.

But what critics see as new about De Sagazan is her theatrical stage shows. She is inspired by Samuel Beckett-style minimalism, she says: bare decor, bold lighting, a bit of steel and concrete as “a souvenir of Saint Nazaire”, and wearing basic black cycling shorts, vest and boots. Her performances deliberately veer from melancholic, pristine, piano ballads to a kind of electro party that gets the audience sweating it out to repetitive beats as if they’re in a Berlin club. She loses herself in freeform dancing, as thousands dance to her anthem for self-esteem: Ne te regarde pas, lache-toi (“Don’t look at yourself, just let go”).

“It’s like dancing in a storm,” she says. “There’s nothing more beautiful than freedom. If things are choreographed, it doesn’t feel so free. I like not knowing what I’ll do.”

All her undulating moves are held up by a very French focus on lyrics. Aspiration is a song about a time when De Sagazan was smoking too many joints and knew she should stop. Its intoxicating dance crescendo has her repeating ma dernière cigarette (“my last cigarette”), trance-like in perfect chanson française diction over a repetitive electro beat. It becomes a desperate metaphor for anything anyone ever wanted to give up: that last drink, last piece of cake, last purchase. “It’s about obsession really,” she says. “I wanted to talk about that addictive spiral. That thing in your head of, ‘It’s my last, last, last, last, last one I promise, then I’ll give up.’”

Her most acclaimed song, Les Dormantes, was written when she was 15 about a teenage friend who was in a toxic relationship experiencing coercive control, and unpicks the mechanisms of being dragged down by a manipulator. “Music and poetry allow you to talk about these things with a bit of distance and theatre,” she says.

De Sagazan’s ironic, pleading lines about l’amour – from the spiky and tortured Suffisament (“You love me just enough to keep me here”) to the riotously upbeat “I’m in love with all the boys” – have seen her praised as one of France’s best modern songwriters on the subject. There’s an irony to this, which is that she says she has never had a serious relationship or even been in love – a fact she likes to announce on stage during her performances.

“There’s a tendency to think love is only romantic love, but there are loads of other types,” she says. “I defend friendship, body and soul, because I think there’s nothing more beautiful.” Writing love songs is like being an actor in character, she says – some songs about imaginary break-ups had her “in tears at my piano”.

But she also thinks art must take a stand. This summer, when Marine Le Pen’s far-right National Rally party surged in the first round of a snap parliament election, she was among the singers who performed at a protest in Paris against their rise. In the end, tactical voting held the party back. “Some people said ‘Don’t talk politics’, but I think in this type of crisis, music is essential,” she says. “It’s not propaganda – I wasn’t telling people how to vote. But the essence of art is sending a message about society.”

At 21, she worked as a carer for elderly and disabled people in the western city of Nantes, where she now lives. “I loved meeting 98-year-olds, it taught me what it was to be human,” she says. But she knows that doing that job “based on kindness”, and not valued or well remunerated by society, is the opposite of now appearing on stage and being adored.

Everything comes back to her lifelong hypersensitivity, the constant tearfulness that drove her to music. She says she has made peace with being sensitive. “I thought it was my biggest flaw but what if it’s actually a great quality? Being sensitive is being alive. If I wasn’t so sensitive, I would never have sat down at the piano and wouldn’t have experienced all these marvellous things.”

• Zaho de Sagazan plays the O2 Forum Kentish Town, London, on 21 October. The international edition of her debut album La Symphonie des Éclairs (Le Dernier des Voyages) is out on 25 October