The closing decades of an artist’s life do not generally make the biographer’s heart beat faster, but Claude Monet is one of a handful of painters who bucks the pattern of an irrelevant old age. While it’s true that by the time he was 73 he had accumulated all the usual dragging baggage – outhouses full of fancy cars, a taste for expensive wine and a sprawl of dependants – it was also now that he produced career-defining work. More specifically, he produced what he called his Grande Décoration, consisting of those eight giant waterlily murals that curve around the Orangerie des Tuileries in Paris.

These canvases were hardly Monet’s first pass at the subject – he’d been doing waterlilies, or nymphéas, for 30 years, in a variety of sizes, colours and shapes. But these are the ones you think of first – huge bruised stretches of purple and green, broken up by sudden splotches of mustard and puce. At the time, critics described the Grande Décoration as “serene”; today they’d probably say “immersive”. But if we’re being honest, we might also call them clammy and uncanny.

The darkness of these late lilies compared with the earlier versions is explained by the trauma of their making, which Ross King makes the subject of this fine, fluent book. Until the moment in 1914 when Monet picked up his paintbrush to begin his final cycle of lilies, it looked as though France’s greatest living artist was going to coast into an anodyne old age. His beloved wife had died three years earlier, his eyesight was clouding with cataracts and he had more than enough money in the bank. On his estate at Giverny, the village 50 miles from Paris where he had settled in 1883, Monet employed six local men to tend his garden and was known behind his back as “le marquis”.

The war changed everything, galvanising Monet into producing a Leviathan piece of painting that stretched eventually to 300 feet. Although he didn’t initially admit it to himself, this was clearly designed as public art, which is why, in 1918, Monet offered it to the nation – and the nation, battered, bruised and in desperate need of a pick-me-up, said yes. For although impressionism, the art movement Monet had spearheaded with Renoir and Degas 50 years earlier, had started to seem passé, its determined insouciance was exactly what was needed now. Monet, after all, wasn’t famous just for painting cathedrals, haystacks and lovely girls in white dresses, but for capturing the sunshine that buzzed around them. It was that sunshine, which spoke of long days at the beach or in the park, that provided the perfect reminder of just what it was that had been at stake during these five terrible years.

The irony was that it soon became apparent that there was nothing remotely optimistic or even particularly French about the Grande Décoration. Throughout the decade during which Monet wrenched it up from his bowels, the “painter of happiness” behaved like someone short of serotonin. He terrorised his stepdaughter Blanche, who doubled as his daughter-in-law and studio assistant. When he got frustrated with a canvas, which was often, he either kicked it with his clogs or ran it through with a kitchen knife. And while there’s no doubting his genuine horror at the fate befalling France – Verdun was less than 200 miles away from Giverny and four members of his family were at the front – it didn’t stop Monet behaving like a spoiled prince while millions of young men were losing their lives. He insisted that he could only work if the government magicked up a steady supply of cigarettes, petrol and coal, the three things he considered essential to his creative flow.

Nor, suggests King, in what is a careful unpicking of cherished art historical narratives, does the provenance of the waterlilies stand up to scrutiny. The pond at Giverny was entirely manmade, created by diverting the water supply from the village (when the locals protested that they needed it for their laundry and cattle, “le marquis” told them to get stuffed). And most of the plants were not native but were hothouse cultivars shipped in from South America and Egypt. In short, the fabled waterlily location at Giverny, far from being a natural outcrop of rural France, was a laboratory in which Monet carefully assembled the colours and shapes to which he required access at a moment’s notice (he maintained that the Normandy light changed every seven minutes and he needed to be on hand to capture it on canvas).

Perhaps the highly confected nature of the Grande Décoration doesn’t matter because, in truth, it is often hard to know what the paintings are supposed to be. The critics, who in the 1870s had puzzled over the blurred outlines of Monet’s sunrises, seascapes and picnicking desmoiselles, would have been completely stumped by it. There is no up nor down in these late waterlily panels but simply passages of colour, sprawls of pigment, localised flurries and bunches of paint. Here is impressionism in its last hurrah, pushed towards its logical destination of abstraction. It’s for this reason that mid-century American artists, including Mark Rothko and Jackson Pollock, found the Grande Décoration such an inspiration: frameless, refusing the eye a resting place, these 22 panels are less about waterlilies or willows or the morning sun than they are about the pleasure of paint.

Readers of biography tend to require more than potted art history to keep them going. Above all, they like love affairs, and those are thin on the ground when the subject is over 80. Luckily for King, there is a candidate on hand for the role of Monet’s petit ami. It comes in the unlikely form of Georges Clemenceau, the politician and wartime prime minister, whose nickname “The Tiger” suggests that he wasn’t a complete sweetheart. Monet, though, was the one person who could make the tiger go soft on the inside. Clemenceau babied Monet through his endless crises, nagged him to see eye doctors, and made sure cigarettes and coal arrived at Giverny on schedule, even while the rest of the country starved and froze. Most important of all, the tiger chivvied his dilatory friend into firming up the timetable for handing over those 22 panels: nearly a decade after the armistice, Monet was still refusing to let them go.

In the end, Clemenceau was obliged to wait until Monet’s death in December 1926 before he could bustle the waterlilies into the Orangerie. It was not, in truth, a particularly glorious moment. All those colourful smudges and loose brushwork seemed vaporous and ephemeral in comparison with the rugged inquiry into form that you got with the cubists and futurists. And the Orangerie was hardly a prestige location, having most recently been used for dog shows. Still, biography loves nothing better than a reputational wilderness, followed by glorious resurrection. In a final chapter, King charts Monet’s gradual postwar rise in reputation, until the point where today he reigns supreme, bobbing far above the vagaries of taste and fashion, and settled comfortably into the realm of the immortals.

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