The son of an electrician, and himself an electrician by trade, O'Neill was largely self-taught, although he briefly attended Belfast College of Art life classes, before working with and studying under fellow Belfast artist Sidney Smith. He quickly developed an expressionist technique, and strong romanticism, with imagery, often full of pathos, evoking the themes of love, life and death. The start of his painting career coincided with the outbreak of World War II and after the 1941 Belfast Blitz he salvaged wood and experimented with wood carving. O'Neill's first exhibition was at the Mol Gallery in Belfast in 1941. Within five years, Dublinart dealerVictor Waddington became involved, resulting in O'Neill having a regular income which allowed him to give up his day-job as an electrician, and focus on painting full-time. In 1946 he sold 21 pictures out of 23 at an exhibition at the Waddington Galleries in Dublin and from then on exhibited regularly. In 1949 he visited Paris and was influenced by Georges Rouault, Maurice de Vlaminck and Maurice Utrillo. A number of works followed on which his reputation largely rests, including: Place du Tertre, The Blue Skirt, Knockalla Hills, Donegal and Birth. His later work, largely brighter in colour, was seen by critics as less successful. In 1951 his work was shown in the Tooth Galleries, London and he also exhibited there with Colin Middleton in 1954. In the 1950s, O'Neill moved from Belfast to Conlig, County Down, where there was a small artist's colony that also included George Campbell and Gerard Dillon. Along with Colin Middleton, Gerard Dillon and George Campbell he was one of a group of artists who respected each other’s work and kept in touch over the course of their careers. However, after the closure of the Waddington Gallery in Dublin, O’Neill found it difficult to exist as a painter. He lived in London from 1958 to 1971 and his work in this period was increasingly introspective and often desolate. In 1970 George McClelland invited O’Neill to exhibit a one-man show, Recent Paintings, at his Belfast gallery, and provided O'Neill with accommodation and a studio to work in. It was his first one-man show in 18 years and was a complete sell out. However, this return to good fortune was not sustained as McClelland Galleries was badly affected by the civil unrest in Belfast in the early 1970s. O'Neill returned to Belfast in 1971, where he died in 1974. During his lifetime, O'Neill's works were primarily exhibited at the Royal Hibernian Academy. More recently, some of his paintings were shown at the Irish Museum of Modern Art as part of a 2005 exhibition of Northern Irish artists. His work is represented in many collections including the Ulster Museum, Queen's University Belfast and the Hugh Lane Municipal Gallery, Dublin.
