William Orpen, the son of Arthur Herbert Orpen, a solicitor, was born in Stillorgan on 27th November 1878. Orpen showed an early interest in drawing and according to his biographer this "was indulged by his mother, who supported his wish to go to art school against her husband's desire that he should study law and enter the family firm."
Orpen entered the Metropolitan School of Art in Dublin at the age of thirteen. During his years at the school Orpen won every major prize available. He then enrolled at the Slade School of Fine Art in 1897. His main tutors were Henry Tonks and Philip Wilson Steer. Orpen's fellow students included Augustus John, Wyndham Lewis. Spencer Gore, Michel Salaman, Edna Waugh, and Herbert Barnard Everett.
Initially, Orpen wanted to be a caricaturist but after having several cartoons rejected by Punch Magazine he decided to return to Ireland to teach at the Dublin School of Art. He returned to London in 1903 where he joined forces with Augustus John to run a short-lived art school in Chelsea. In 1906 he also helped to set up the Chenil Gallery with his brother-in-law, Jack Knewstub.
In 1908 Orphen exhibited for the first time at the Royal Academy. This helped to develop his reputation as a portrait painter. In 1916 Orpen's friend, the Quartermaster General, John Cowans, arranged for him to receive a commission in the Army Service Corps. This mainly involved him painting the portraits of senior political and military figures such as Winston Churchill and Lord Derby.
In early 1917, Charles Masterman, head of the government's War Propaganda Bureau (WPB) recruited Orpen to produce paintings of the Western Front. His biographer, Bruce Arnold, points out: "He left for France in April 1917, and for the next four years was totally immersed in the war and its aftermath. His output, and its overall excellence, makes him the outstanding war artist of that period, possibly the greatest war artist produced in Britain. Analysis of his war work, the major part of which is in the Imperial War Museum, London, shows a development in style and understanding, from the idealism which inspired him when he first arrived at the front to the disillusionment with the terrible ending to the war, and then the further dismay he and many felt at the direction taken by the peace deliberations. His paintings of the Somme battlefields are haunting recollections of anguish and chaos, of ruined landscapes baked in the summer sun, the torn ground white and rocky, the debris of the dead scattered and ignored."
While in France he painted portraits of Sir Douglas Haig, Hugh Trenchard, Herbert Plumer, Henry Rawlinson, Henry Wilson, James McCudden, Arthur Rhys-Davids, Reginald Hoidge, John Edward Seely, John Cowans, Adrian Carton de Wiart, and Ferdinand Foch. Orpen was shocked by what he saw at the front and also painted pictures such as Dead Germans in a Trench. Other paintings such as The Mad Woman of Douai, "convey the stress and anguish he certainly felt about the war and its aftermath".
Orpen was commissioned to paint portraits of the politicians at the Versailles Peace Conference. He also produced a series of caricatures that according to the author of the Dictionary of Twentieth-Century British Cartoonists and Caricaturists (2000) "were widely admired". Orpen believed that the soldiers that fought in the war were betrayed by the politicians at Versailles. Instead of the portraits he painted To the Unknown British Soldier in France. The original painting showed the draped coffin flanked by two shell-shocked soldiers standing guard. There was such an outcry when it was exhibited in 1919 that Orpen was forced to paint out the soldiers. However, as one critic has pointed out "their shadowy forms remaining as ghostly pentimento."
Orpen wrote about his experiences in the First World War in An Onlooker in France (1921). Bruce Arnold has argued: "His outspokenness became controversial. His standing as a painter gave him the ear of many people in power, and he took risks, confronting what he saw as foolishness.... His own personality had developed with the war; his early idealism became a form of sombre realistic recognition of the terrible path of war through the lives of a whole generation. He came to love the fighting man, and to despise the politicians, with their glib words and their self-interested carve-up of Europe which was subsequently to prove so disastrous."
An exhibition of Orpen's war paintings were well received. Arnold Bennett argued: "William Orpen, having discovered a new subject, composes it newly.... Landscape, shell-holes, ruined trees and buildings, dug-outs, tents, and the tragedy and comedy of human existence - he see them as though nobody had ever seen them before; and he arranges them in fresh patterns of contour, colour, plane. His ingenuity in manipulating the material is simply endless, and yet he is never tempted to falsify the material."
Orphen became known for his portraits of public figures and during his career produced over 600 of these pictures. Mark Bryant has pointed out: "However, though he was financially very successful in his main occupation as a portrait painter (reputedly earning more than £54,000 in 1929 alone) his technique of using photographs as an aid did not meet with universal approval."
Sir William Orpen died from liver and heart failure on 29th September 1931 at his home in South Kensington. He was buried in Putney Vale Cemetery.