M‘Neile's father owned considerable property (including the large farm at Collier's Hall), was a Justice of the Peace and served as the High Sheriff of the County of Antrim. His brother, John M‘Neile (1788–1855), having made his fortune in South America, returned to Ireland and was one of the founding members of the Northern Bank, the first bank in Belfast. John M‘Neile married Charlotte Lavinia Dallas (1803–1859) on 11 June 1823 and had two sons, Henry Hugh (1829–?) and Alexander John (1842–?) and one daughter, Mary Harriet (1833–1919), who married Hugh McCalmont Cairns (1810–1885), the First Earl Cairns, who served as Attorney General in the third Derby–Disraeli ministry (10 July 1866 – 29 October 1866), as Lord Chancellor in the first and second Disraeli ministries, and as (opposition) Conservative Leader in the House of Lords (1869–1870).