The Honorable Arthur Edward Bruce O'Neill (19 September 1876 – 6 November 1914), was an Irish Ulster Unionist Party politician who was the first Member of Parliament to be killed in World War I. O'Neill was the second but eldest surviving son of Edward O'Neill, 2nd Baron O'Neill, and his wife Lady Louisa Katherine Emma (née Cochrane). Hugh O'Neill, later Baron Rathcavan, was his younger brother. Arthur O'Neill was elected to the House of Commons for Mid-Antrim in 1910, succeeding his uncle Robert Torrens O'Neill. O'Neill fought in the First World War as a Captain in the 2nd Life Guards and was killed in action at Klein Zillebeke ridge, 6 November 1914, aged 38, the first MP to be killed in the conflict. His brother Hugh succeeded him as MP for Mid-Antrim.