How to blow it

Visual art - Simon Poe on the tragicomic death-in-life of a genius who lost his way

William Orpen was a successful outsider, an Irishman who made it to the heart of the British establishment. He was a Royal Academician, knighted in 1918 for his contribution to the war effort after a hugely successful exhibition of his images of the Western Front. He made more money from painting than any other artist of his generation. After his death in 1931, however, his colossal reputation evaporated almost overnight, as the triumph of modernism swept British art off in another direction.

A show at the Imperial War Museum London offers a British audience the first chance in 70-odd years to form an opinion of his work. The exhibition has the exciting subtitle "politics, sex and death", but can a display of paintings by a half-forgotten artist fulfil the expectations this arouses?

Orpen disliked it when conversation took too serious a turn, and was known to get down from the dinner table and crawl around yapping like a dog when he thought pomposity needed deflating. And yet, when he quipped that although he had been brought up on the "Irish Question" he had no idea what the question was, he was being disingenuous: pictures in one section of the show demonstrate that he took a serious interest in the politics of Irish nationalism. Politics and death meet in his war paintings and his bitter documents of the peace process; and politics, in a less specific sense of the word, pervades most of the exhibition.

In one of the show's highlights, the magnificent conversation piece Homage to Manet, Orpen records and supports the successful campaign of his compatriot Hugh Lane to bring impressionism to Dublin. In this image, a group of contemporary taste-makers, a cabal of art-world politicians (Lane, the painter and teacher Henry Tonks, fellow artists Walter Sickert and Philip Wilson Steer, the writer D S MacColl), gather under Manet's portrait of Eva Gonzales to hear George Moore read his Reminiscences of the Impressionist Painters. Sly portraits of his contemporaries Augustus John and William Nicholson, intended to wound, are an index of Orpen's rivalries.

Orpen was very short and not at all handsome. As a boy, he overheard his parents wondering how he came to be so ugly when his siblings were all so good-looking, an experience that understandably left a scar. However, he was obviously attractive to women and had a succession of lovers, many of them bigger than he was. The American millionairess Evelyn St George, at over six feet, towered above him (they were known as "Jack and the beanstalk"), and the tough Frenchwoman Yvonne Aubicq used to knock him about.

Orpen was an obsessive self-portraitist, frequently representing himself in cos-tume, as a jockey, as a huntsman, or even as the painter Chardin (dressed in the costume in which he had won a prize at the Slade School of Fine Art fancy-dress ball), and his self-image is truculent, often uglier than the reality. Mirrors abound in these paintings, which are full of echoes, reflections and puns. Orpen's mastery of technique is awe-inspiring, but the impression given is not of an artist unselfconsciously testing himself, but of a show-off determined that no one will fail to notice how clever he is.

In 1917, Orpen went to France as an official war artist, and the charming playfulness of his early work, as well as that tiresome clever-cleverness, seems to have been burnt out of him by the horrors of the front. He developed a lurid new palette to represent the blasted landscape, but perhaps his simple pencil drawings, such as The Manchesters, Arras, of a young man with dead eyes and a cigarette, show him at his most effective.

Orpen identified strongly with the men and against the "brass hats" and politicians. He stayed in France to paint the peace talks. The master of mirrors was the perfect artist to paint The Signing of Peace in the Hall of Mirrors in Versailles on 28 June 1919, representing "the frocks", as he called the men in suits, dwarfed by the architecture in a richly symbolic image fractured by multiple panes of glass. He did not finally return to England until 1923, but stayed in Paris with Aubicq. The glorious, sunny, sexy painting of her, Early Morning, belongs to this period.

Orpen never really recovered from his war experiences, but subsided into the artistic death-in-life that is a fashionable portrait practice. Because he was something like a genius, he made a huge success of it, drank a bottle of whiskey a day while the Rolls-Royces queued up out-side his studio, and died, rich and pickled, of heart failure at the age of only 53. His career was a tragicomedy, and he seems not to have been at all a nice man, but his work is far too good to remain any longer in obscurity.

"William Orpen: politics, sex and death" is at the Imperial War Museum, London SE1 (020 7416 5000) until 2 May and at the National Gallery of Ireland, Dublin (+353 1 661 5133) from 1 June to 28 August