(b Milton, Co. Roscommon, 17 Oct. 1860; d Nueil-sur-Layon, nr. Saumur, 18 Mar. 1940).
Irish painter and etcher, active for most of his life in France (mainly Paris), where he settled in 1883 after studying in London and Antwerp. He was strongly influenced by Gauguin and van Gogh, and by the early 1890s was painting in a full-blooded Post-Impressionist style marked by bold colour—often used non-naturalistically—and thick brushwork. He lived a fairly reclusive life (although he was friendly with many British visitors to France, including Clive Bell and Roger Fry) and he was virtually unknown in the British and Irish art worlds. It was only after his death that he was recognized as the leading pioneer of Post-Impressionism among English-speaking artists. He did, however, notably influence Matthew Smith, whom he met in 1919. O'Conor was mainly a landscapist, but he also painted still lifes, portraits, interiors, and figure subjects.