The Singer (12A)

We can precisely identify the moment when it became impossible to take Gérard Depardieu seriously. It was a Reeves and Mortimer sketch, in which a mountainous figure loomed in Cyrano de Bergerac's cloak and hat, while the comics sang, "Somebody obscures my view of you! – Really, who? – Gérard Depardi-oo!" The last decade has not done much for the dignity of the Greatest French Actor of his Generation: the macho muse to Bertolucci, Truffaut, Resnais et al has preferred to spend his time being Obelix the beefy Gaul in the Asterix films, playing joke French chefs in Queen Latifah comedies, and waxing poetic in a vanity cookbook ("Cooking is all about love, and love is strength").

We've grown so used to this over-prolific toiler wasting himself in dud after dud that these days, people regard it as a significant comeback if he merely turns up to scowl in a so-so French thriller such as the recent 36. Still, you sometimes catch yourself thinking, wouldn't it be great if Depardieu could find a role he actually cared about. Well, tiens voilà, here's such a film – Xavier Giannoli's The Singer.

At first sight, this is a low-key, unambitious affair, a good-natured character study with a dash of melancholy May-September romance. But really it's far subtler than that, and for once, Depardieu gives so much that he effectively turns the film into an essay on himself: I'm not being uncharitable if I say that The Singer is a portrait of the artist as a weary but likeable ham.

Depardieu plays Alain Moreau, a singer-bandleader who's a minor local celebrity in the French town of Clermont-Ferrand, where he presides over weddings, dances and town hall functions. Purveying a repertoire of variously cheerful and sentimental cover versions, he's the man whose job it is to thank the mayor, get people on the dance floor and remember to announce the tombola. It's not an edifying job, but he does it with resilience and bonhomie. He's not an artist by any means, and he knows it, but he's a pro – and he draws the line at "The Birdie Song".

Then one night, estate agent Marion (a crisp, snootily fragile Cécile de France) walks into one of his events, and Alain is taken by her brittle cool. She's not impressed by this bulky charmer's ancient, mechanical chat-up lines, yet somehow – in a liaison as improbable as the one in Knocked Up – she falls into his arms, then runs like hell in the morning. Alain knows he's no catch, but he's mortified to see how coolly Marion treats him. Then he starts hanging around her on the pretext of shopping for a new home, although his crumbling farmhouse, where he lives with a drum kit and an indoor goat, looks like all any man could want.

The thorny relationship between Alain and Marion – whose own life crisis Giannoli sketches with detached reserve – modulates surprisingly over the story's length, complete with emotional twists that are often all the more effective for skirting crassness. One nightclub scene has Alain singing a slow, maudlin "Save the Last Dance For Me", while Cécile whirls in the arms of a younger, smoother admirer. The scene could have been excruciatingly cheesy, yet it's incredibly poignant because we sense that both Alain and Marion know that they're living out a cliché, and are pained by it. At one point, Alain, defending his craft, says: "To me, all songs tell the truth – especially if they're sentimental." It's a cheesy observation, part of Alain's third-rate showbiz philosophy, yet it's a notion that the film is prepared seriously to entertain.

What allows Giannoli to milk cliché for emotional truth is his respect for his characters. You can imagine what a British or American treatment of this theme would be: as nudgingly campy as Adam Sandler's The Wedding Singer or as contempt-laden as Steve Coogan's Eurovision dolt Tony Ferrino. But Giannoli's film isn't about a second-rater, it's about someone who is competent in a faintly ridiculous profession.

Our first glimpse of Alain – a priceless mugshot of Depardieu simpering over a long-stem rose – makes us think that we're in for a send-up, but this is nothing of the kind. Giannoli respects – rather than reveres – the French MOR songbook, and Alain's repertoire mixes numbers that are respectable, borderline dreadful, cheerfully toe-tapping, and faintly embarrassing yet never so abject that you cringe.

Depardieu sings them himself, in an unshowy, affable way that suggests he's hung around a few wedding parties and studied mike technique: let it be said, his laconic reading of Serge Gainsbourg's "L'Anamour" is very good indeed.

Of course, Depardieu very much looks as if he's playing himself, gently mocking our perception of him as a jaded, buffoonish hack. Alain knows that Marion thinks he's "corny", as the subtitles put it – the French adjective "ringard" has connotations of shop-soiled loserdom – but he tells her, "People become corny when they last," a line that Depardieu can console himself with in his fifth decade on screen.

Alain's life might look sad – broken marriage, afternoons serenading OAPs, a chilling brush-off from a young backing singer – but Depardieu gives him dignity through magisterial downplaying: where the role could have accommodated ingratiating bluster, Depardieu simply makes Alain a soft-spoken, quietly ironic man.

The actor has no qualms about being shot unflatteringly from the side, or about looking grey and bulky in tie-dye shirts and aviator shades, lumbering heavily across a disco car park at dawn. Besides, if Alain looks ridiculous, it's because he's the last man in France wearing that once-modish floppy Depardieu haircut.

The film's French title is Quand j'étais chanteur – When I was a singer – and the past tense is crucial. It comes from a mid-70s song by Michel Delpech, a self-mockingly nostalgic ballad from the point of view of a septuagenarian ex-crooner whose glory days are gone, but who prides himself on having outlived Mick Jagger. Depardieu sings it in the end credits – following a world-class lump-in-the-throat denouement – and his rendition not only brings this magnificently bittersweet film into sharp emotional perspective, it leaves you humming the tune on the way out.

When the film premiered last year in Cannes, the world's most blasé festival audience actually clapped along to the credits. Some British critics took this as confirmation that the film was an unbridled display of Gallic corniness. But there's nothing remotely corny about The Singer: rather, Giannoli's film is an exceptionally astute anatomy of corniness, of the way it keeps people afloat through mundane, disappointing lives.

Now, when Depardieu goes back to whatever he most enjoys – tending his cru, bashing up cartoon Romans, or perfecting his Rum Baba With Crystallised Pineapple – he can be content to know that in The Singer, he's created a late-period role that's up there with his best.

Further reading More than just cheese and ham? 'Gérard Depardieu: My Cookbook' (Conran Octopus, £20)