O'Neill, Robert William Hugh (1883–1982), 1st Baron Rathcavan and politician, was born 8 June 1883 at Shane's Castle, Co. Antrim, third son of Edward Chichester O'Neill, 2nd Baron O'Neill of Shane's Castle and former MP for Co. Antrim (1863–80), and his wife, the former Lady Louisa Cochrane, daughter of the 11th earl of Dundonald. Hugh (as he was always called) was educated at Eton and New College Oxford, where he graduated BA (1905). The following year he contested the Stockport division of Cheshire as a tory and was defeated. In 1909 he was called to the bar at the Inner Temple. On the outbreak of the first world war he was already a member of the Imperial Yeomanry and soon afterwards he accompanied the 12th Battalion, Royal Irish Rifles, to France as adjutant-major. He was later awarded the French Ordre de Mérite Agricole for wartime services. His brother Arthur Edward Bruce O'Neill (1876–1914) had been elected to the family seat of Antrim Mid in 1910, but on 6 November 1914 became the first MP to be killed in the war; the following year Hugh O'Neill was returned to his seat. He sat for Antrim constituencies in Westminster for thirty-seven years: mid-Antrim (1915–22), Antrim (1922–50), and Antrim North (1950–52).
O'Neill spent 1918 in Palestine as deputy judge advocate general. On his return to Britain he threw himself into the unionist movement. He had pinned his hopes on the 1917 convention and was dismayed by its collapse; he afterwards backed partition. Elected to the first Northern Ireland parliament for Antrim (1921–9), he was also speaker of the house for that period. After relinquishing the Stormont seat, he concentrated his parliamentary career in Westminster, was chairman of the Conservative 1922 committee (1935–9) and parliamentary under-secretary for India and Burma (September 1939–May 1940), and after thirty-six years of consecutive service became father of the house in October 1951. He retired from the commons in 1953 and was created 1st Baron Rathcavan (11 February 1953).
O'Neill was an Orangeman who viewed the Irish Free State as ‘a small, petty, insignificant, so-called republic, divorced from all the great world movements’ (Times, 30 Mar. 1932). He was inclined to blame Northern Ireland problems on the catholic minority, an attitude that may have been cemented by the IRA burning of the family seat, Shane's Castle (1922). During the 1930s he privately told a friend, Henry Dobbs, that unionists were being saddled with too much blame for the current unrest, when the responsibility really lay with catholics, and in particular with gangster elements. This position was publicly reiterated in one of his last speeches in the commons (1 June 1951), when he claimed that catholics got every chance in Northern Ireland but chose to remain aloof and nurse grievances.
He was lord lieutenant for Co. Antrim 1949–59 and afterwards retired from public life, dying in London on 28 November 1982. He married (11 February 1909) Sylvia Irene Sandeman (d. 19 July 1972) of Hertfordshire; his third son also predeceased him, but he was survived by his elder sons, Phelim Robert Hugh O'Neill (qv), NI minister of education and agriculture 1969–71, and Sir Con O'Neill (qv), a diplomat who negotiated Britain's entry to the European Economic Community in 1972.