Jack Yeats lived his life in the shadow of his elder brother, the poet, the famous W B. Yeats, who was to become Ireland’s greatest painter, was born in London in 1871, at Fitzroy Road, Primrose Hill, the fifth of John and Susan Pollexfen Yeats’s six children. The family were dragged from Ireland to London when the wayward father abandoned the prospect of a lucrative career as a Dublin barrister in favour of painting among the London Pre-Raphaelites. The four surviving Yeats children (two died in infancy) spent their London years longing for Sligo, their mother’s birthplace, where they spent the summer.

Only Jack got to live there full-time. Exiled, as the youngest children in large families often were, he spent his boyhood with his maternal grandparents. The dark, glowering beauty of the west of Ireland seeped into his soul and into the sketches and drawings he began at an early age. So did its desolation. In 1915 Jack had a nervous breakdown, from which he was several years recovering. The collapse was attributed to the poor sale of his work. But the family knew that genes played a part. The Pollexfens, although practical merchants and shipowners, were an unstable lot.

Bruce Arnold has chosen a good time to bring out this massively detailed biography, drawing on the vast archives preserved by his subject’s niece, Anne Yeats. Jack Yeats’s work is appreciated as never before. He is now seen, Arnold says, as having painted Ireland into an existence it did not previously enjoy. He is as original and unmistakably Irish as Synge, with whom he toured Connemara and Mayo in 1905 on a commission from the Manchester Guardian. Like Synge, Yeats focused on the peasantry, but he was captivated also by the jockeys, the hurlers, the seamen and the clowns. There are few women in his Ireland, which is a world of men and horses.

Arnold’s book is timely, too, in following the first volume of Roy Foster’s authorised biography of W B Yeats. Never has it been so clear what Jack had to struggle against: not only the towering reputation of his brother but also the miserable family scene – the irresponsible if gifted father; the mother depressed and silent even before she was paralysed by strokes; the sisters doomed to spinsterhood by the lack of a dowry and the need to work to support the hungry household. Rejoining this unsettled family after his Sligo years, Jack shared their various London residences, from Earls Court to Bedford Park. He attended four London art schools, in South Kensington, Chiswick, West London and Westminster. He got himself out of the nest early. At twenty-three he married, using his decent earnings as a cartoonist and illustrator for The Vegetarian, Paddock Life and the Manchester Guardian to buy his freedom (and also to buy medical treatment for his afflicted mother). His first one-man show, of Irish scenes and Irish life, was well received in 1897 but tagged as the work of W B Yeats’s brother.

The wife Jack chose, after three years’ engagement and sensible saving, was a well-to-do Englishwoman, Mary Cottenham White, known to the family as ‘Cottie’, a fellow art student. She moved with him to Chertsey, then Devon, then Ireland. They were a childless, devoted couple; upon her death in 1947 he was bereft.

Like his brother and sisters, whose Cuala Industries produced fine printing and embroidery, Jack was, in today’s jargon, multi-medial. His vast output included plays and novels as well as drawings, watercolours and oils. He wrote and illustrated his own books as well as Cuala Broadsheets. A special passion, poignant considering his childlessness, was miniature theatre. He would cut out the actors, make the stage, colour the scenery, light it with candles, write the plays, and perform them for children. And, like his brother, he succeeded on both sides of the Atlantic, thanks to the influential Irish-American patron John Quinn. In 1913 five of his paintings, including The Circus Dwarf, were shown in the celebrated Armoury Show in Manhattan.

A great Irish nationalist, Jack returned to live permanently in Ireland long before his brother Willie did. He allied himself on the anti-British side in 1914 with a painting, Bachelor’s Walk: In Memory, honouring those shot by soldiers after a gunrunning incident on Howth Quay. The painting became a nationalist icon. When the Civil War broke out, the brothers were on opposite sides – Willie pro Treaty and a Senator in the Free State, Jack anti-Treaty and pro Sinn Fein. There was coolness between them – but no more than that – for years.

Like his brother, Jack Yeats was large (size 17 ½ collar, chest 46). He, too, blossomed in old age, although, unlike Wilde, who was preoccupied by sex in his later years, Jack seemed oblivious to it. He became a close friend of Samuel Beckett. In 1936 Beckett said of Jack’s painting of Sligo, called Morning: ‘It’s a long time since I saw a picture I wanted so much.’ (The painting is now in the National Gallery of Ireland.)

In 1940 Jack formed the relationship with Victor Waddington that was to establish his reputation in Britain. In the catalogue for an exhibition in 1942 at the National Gallery in London, Kenneth Clark, the curator, said: ‘We follow Jack Yeats breathless and a little drunk’ (and Clark bought one of the paintings too). This was followed by a one-man show at the Waddington Galleries in 1943.

Yeats’s canvases got larger as the artist shifted from the anecdotal to the symbolic. High honours arrived – late, but well before his death in 1957. In 1945 he was honoured as Ireland’s greatest living painter with a retrospective exhibition in Dublin’s National College of Art. An honorary doctorate was awarded by Trinity College, Dublin, in 1946 (his brother’s had come in 1922); in 1950 a Légion d’honneur. Dublin’s Peacock Theatre performed his last play, In Sand, in 1949.

Bruce Arnold doesn’t get to the bottom of this curious, taciturn yet sociable genius, but he thoroughly captures the complex, confusing, colourful surface. The Jack Yeats he gives us is ‘inscrutable and enigmatic’, a man who painted in solitude – no one saw him do it – and whose technical defects (gloomy colour, heavy line, poor composition) keep him from the very top rank. Yet Arnold gives us a powerful artist, a masterly conveyor of the spirit of Ireland, and a kindly man. The copious illustrations are reproduced with Yale University Press’s usual elegance.