Which of all the British poets came from the most deprived background? Thomas Traherne? William Blake? John Clare? Robert Burns? Almost certainly the correct answer is Isaac Rosenberg, who was born into a family of Yiddish-speaking Lithuanian Jewish immigrants in 1890. His father was a pedlar; his mother took in washing and sold fancy needlework. The first London home they found for themselves and their five children was a single room behind a rag-and-bone shop in Tower Hamlets. Later they moved to a ground-floor and basement in Whitechapel. Isaac had a twin brother who died soon after birth, and he was so small a baby that, as his mother enjoyed recalling, “you could have put him in a jug”. Like many slum children, Isaac grew up stunted and with a weak chest. He started school aged eight, unable to read or write English, but reached the required grade in the three Rs within a year, and moved to one of the board schools established under the 1870 Education Act. In effect, it was a Jewish school within the state system, and he learnt some Hebrew and Old Testament history. But the education was basic at best (no foreign languages, no music) and he had to leave to earn his living at 14, getting a job in an etching workshop, which he hated.

His literary and artistic gifts became apparent early on. His sisters remember him writing poems in bed by the light of a candle, and sketching complete strangers on street corners. His studio was the kitchen table, littered with cups and plates. By the time he was 11, he had become an accomplished watercolourist, and efforts began to be made on his behalf, driven by community spirit, family solidarity and an earnest belief in education - all of them things we seem to have abandoned. The Jewish Education Aid Society took a hand, so did his teachers and private Jewish benefactors. Means were found to send him to Stepney Green Crafts School for one day a week, then to evening classes at Birkbeck College, and, in 1911, to the Slade School of Fine Art. Most of his fellow students were upper middle class, and their recollections of him focus on his “appalling cockney accent”, bad adenoids and “shocking teeth”. He tried reading them his poems, but they bombarded him with paper pellets, and when he lent some of them his studio they smashed it up in a fit of high jinks.

He made friends with the painters David Bomberg and Mark Gertler and, together with the poet and publisher John Rodker and the dancer and actress Sonia Cohen, they formed the nucleus of what became known as the Whitechapel Group. They would meet in the Whitechapel reference library, which was warmer and better lit than their homes, and go for all-night walks in Epping forest, talking of “life, death, youth and love”. Jewish, educated at board schools, and forced to work long hours at menial jobs, they were, as Jean Moorcroft Wilson points out, the polar opposite of the privileged and largely anti-semitic Bloomsbury Group.

Her biography of Rosenberg is admiring and devotedly researched, yet critical of his character. She finds him self-pitying, defiant, difficult to help, and ungrateful to his patrons. He was, she admonishes, “in no position to be proud”, and should have behaved better. But is pride to be reserved for the wealthy? Rosenberg's refusal to be obsequious was part of his indomitable self-belief. No doubt it disadvantaged him financially. In the nine months he spent in South Africa, staying with his sister Minnie, he was taken up for a time by well-heeled members of the novelist and political activist Olive Schreiner's circle. But he severed the connection because, for someone of his class, living among “toffs” could only involve “fibs” and dissimulation. He got a commission to paint a leading Cape Town businessman, but chucked it on the grounds that his sitter looked too prosperous. That might be viewed as foolish, or alternatively as the index of a free spirit, and of a conviction that art is only soiled by association with great wealth.

The same independence distinguished his army career. He joined up not out of patriotism, since he felt none, but because the army would clothe and feed him, as writing and painting had failed to do, and would enable him to send half his pay home to his mother. Unlike the more famous war poets, he did not become an officer. Posted at first to a Bantam battalion, for men under 5ft 3in in height, he moved fairly rapidly from unit to unit, accompanied by complaints that he was unsoldierly and neglectful of his duties, which was another way of saying that he had the courage to resist the military machine. “I am determined,” he wrote, “that this war, with all its powers for devastation, shall not master my poeting.”

He showed his intransigence in his poetry, as in all else. Even his friends and admirers were daunted by its obscurities and contortions, which sometimes suggest an imperfect grasp of English usage. Yet he could also write with brilliant clarity, as in Break of Day in the Trenches, which Paul Fussell in The Great War and Modern Memory selected as the greatest poem to come out of that monstrous slaughter. Poised and ironic, it expresses Rosenberg's sense of detachment as he addresses a “queer sardonic rat” that has touched his hand as he plucks a poppy from the trench parapet to tuck behind his ear, and that may go on to touch German hands: “Droll rat, they would shoot you if they knew/ Your cosmopolitan sympathies.”

The perfect corollary of this poem is the self-portrait now in the National Portrait Gallery, which gives a quizzical, confident, sideways glance at us, and the mess we have made of our world. It is only one of a marvellous series of portraits in oils, pencil and other media, not just of himself but of his father, his sister, Sonia Cohen, and of the actress Marda Vanne with whom he may have had a brief affair in Cape Town. He went on doing drawings of himself when he was at the front. One, in black chalk on brown wrapping paper, shows him in an elegant-looking steel helmet.

He was killed by a German raiding party at dawn on April 1, 1918. His body was never found. The headstone in the Bailleul Road East military cemetery in France stands over an empty grave. Moorcroft Wilson's account, incorporating new findings, is the fullest we are ever likely to get of his life. But even if it were less full it would be well worth buying for its splendid reproductions of his drawings and paintings, many of them now unviewable in private hands, which proclaim his unique genius even more distinctly than his words.

Isaac Rosenberg: The Making of a Great War Poet: A New Life by Jean Moorcroft Wilson

Weidenfeld £25 pp480

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