O'Neill, William Chichester (1813–83), 1st Baron O'Neill , clergyman, was born William Chichester 4 March 1813 at Culdaff House, Co. Donegal, eldest among four sons of the Rev. Edward Chichester, rector of Kilmore, Co. Armagh, and Catherine Chichester (née Young). Educated at Foyle College, Londonderry, and Shrewsbury School, he entered TCD (1830), becoming a scholar (1833) and graduated BA (spring 1836). Having followed his father into the church, he was ordained in 1837, and served as prebend of St Michael's, with a stall in Christ Church cathedral, Dublin (1848–59). A devout clergyman, he wrote a number of books, including Friendly suggestions on Christian consistency (1847), and Essays and addresses on the truths of the Christian religion (1886). He was also a talented musician, playing the organ, violin, and piano, and was a prolific composer of church music, glees, and songs. In 1855 his second cousin twice removed, Viscount O'Neill, died and he succeeded to the O'Neill estates in Co. Antrim, including Shane's Castle, and by royal licence took the name of O'Neill in place of that of Chichester. The inheritance included 65,919 acres in Co. Antrim, and in 1883 provided an income of £44,000 a year.
In recognition of his support of the conservative government, on 18 April 1868 he was created Baron O'Neill of Shane's Castle. Bishop Wilberforce met him later in the year and was impressed that he was still ‘simple, humble, and unpretending’ (Hamilton, xxi). When Prince Arthur (later duke of Connaught) visited the castle in 1869 O'Neill was asked to compose poems and music in his honour. In 1875 O'Neill became a founding member of the Victoria Institute, to investigate scientific and philosophical questions, especially those with a religious significance. In 1880 he delivered a controversial address on the action of will in the regulation of the universe, and followed this in 1881 with a paper arguing for ‘The credibility of the supernatural’. He died 18 April 1883 at Shane's Castle and was buried at Drumaul, Co. Antrim.
He married first (3 January 1839) Henrietta Torrens (d. 1857), daughter of Judge Robert Torrens (qv); they had three sons and one daughter. He married secondly (8 April 1858) Elizabeth Grace Torrens, daughter of Dr John Torrens, archdeacon of Dublin; there were no children from the second marriage. His eldest son, Edward Chichester (1839–1928), who also took the surname O'Neill in 1855, was MP for Co. Antrim (1863–80), and succeeded as 2nd Baron O'Neill in 1883.