Sir William Orpen, in full Sir William Newenham Montague Orpen (born November 27, 1878, Stillorgan, County Dublin, Ireland—died September 29, 1931, London, England), British painter best known for his vigorously characterised portraits; he also worked as an official war artist during World War I.
Orpen studied drawing at the Metropolitan School of Art in Dublin (1894–97) and at the Slade School of Fine Art in London (1897–99). He first exhibited at the New English Art Club; he became a member there in 1900. His portraits, which established his reputation, showed the influence of the Realist artist Édouard Manet. He also became known as a painter of group portraits such as Homage to Manet (1909), in which he portrayed members of the contemporary English art world sitting in conversation beneath a famous portrait by that artist. Orpen was the official painter of the Paris Peace Conference after World War I, for which he painted The Signing of the Peace Treaty at Versailles (1919–20).
Orpen was appointed knight commander of the Order of the British Empire in 1918 and was elected a Royal Academician in 1919. He is posthumously regarded as a facile and prolific, but somewhat superficial, artist who nevertheless achieved great popularity in his day.