One day when he was looking along his bookshelves, Mark Hussey realised that they contained no biography of Clive Bell. You can see why it would strike the distinguished Bloomsbury scholar as odd. Over the past 50 years a veritable industry of gossipy life-writing has grown up around even the most minor denizens of early-20th-century WC1, to the point where someone who danced with a man who danced with a woman who danced with Leonard Woolf (assuming Woolf ever kicked up his heels) can boast at least two fat biographies bristling with footnotes.

So why is Bell so Lifeless? After all, he belongs to the innermost circle of Bloomsbury, being both married to Vanessa Stephen and, unusual in a culture that made a point of not worrying what others thought, addicted to public utterance. Indeed, for many years Bell was a fixture in the press, at opening nights and, later, on the Third Programme at the newly minted BBC. While his family and friends wrote, painted, danced and bedded their way into the 20th century, it was Bell’s job to explain to the world just what they were doing and why it mattered.

Bell performed his project of, to use Hussey’s subtitle, “making modernism” chiefly through the championing of “modern art”. By this he meant painting that eschewed anecdote, nostalgia or moral messaging in favour of lines and colours combined to stir the aesthetic sense. For ease of reference, he called the thing he was after “significant form”. While sensible Britain saw cubism, together with post-impressionism, as incoherent and formless to the point of lunacy, Bell followed the example of the older and more expert critic Roger Fry in reframing these movements as heroic attempts to purge the plastic arts of any lingering attachment to representational fidelity. His great touchstones were French (he called Paul Cézanne “the great Christopher Columbus of a new continent of form”) but admitted that occasionally you found an English painter who was making the right shapes – Vanessa Bell, say, or Duncan Grant. The fact that Vanessa was his wife and Duncan her lover detracted only slightly from his pronouncements.

Still, what Hussey wants us to see in this revelatory book is just how different, how much of an outsider in Bloomsbury Clive Bell really was. Unlike the Stephens, Lytton Strachey, EM Forster or John Maynard Keynes, he was not a member of London’s liberal intelligentsia by birth. Rather, his family lived in rural Wiltshire, exactly the kind of hearty, philistine people at whom Bloomsbury curled its collective lip. Even better (or worse), the Bells weren’t really squires, but actually rich industrialists who had made their money from south Welsh coal. Then again, although Bell was bright, he was not super smart. At Cambridge, where he met Vanessa and Virginia Stephen’s brother Thoby, he was never asked to join the Apostles, the elite chatterati to which Strachey, Keynes and the rest belonged.

And finally, above all, Bell was straight. Not just exclusively heterosexual, but doggedly, ponderously and, in time, embarrassingly so. While the rest of Bloomsbury’s men and women moved ambiguously between genders, performing dizzying dances of desire both illegal and scandalous, he ploughed on like a bulldozer, looking for a series of substitute wives, now that Vanessa was committed to life with Grant. As he got older, Bell made excruciating stabs at trying to be groovy – angling for an invite to the infamous Bath and Bottle party of 1928, taking cocaine in Vita Sackville-West’s Long Barn, dad-dancing with girls young enough to be stepping out with his own grownup sons.

While none of this may sound very edifying, it provides a fascinating starting point for Hussey’s meticulously researched and hugely well-informed account of how modern art entered the British bloodstream in the first decades of the 20th century. The peak of Bell’s influence came in 1914 with the publication of Art, in which he introduced the concept of significant form to a general readership. Predictably, the book brought him as much opprobrium as praise, especially when it emerged that its author was a noisy pacifist and conscientious objector. (Bell’s father, with a pleasing symmetry beloved by biographers, had just been made the martial-sounding Lord High Sheriff of Wiltshire.)

You certainly don’t end Hussey’s biography liking Bell. At times he seems to combine bad bits of cliquey, snobbish Bloomsbury with the even worse parts of anti-Bloomsbury – hearty, noisy and frequently brandishing a brace of dead partridge. Still, Hussey’s patient recuperative work is important in reminding us that the significant players in last century’s art history often refuse to fit our sentimental requirements. Bell was no one’s idea of mad, bad or dangerous to know, yet his very ploddiness and clumsy bonhomie proved to be a brilliant camouflage. He is best thought of as a sort of Trojan horse, a plausible cover for a radical programme of aesthetic reform designed to wean middle Britain off its nostalgic attachment to Constable’s clouds and Turner’s sunsets.

• Clive Bell and the Making of Modernism: A Biography by Mark Hussey is published by Bloomsbury (£30). To order a copy go to guardianbookshop.com. Delivery charges may apply.