John O'Neill, 1st Viscount O'Neill PC (16 January 1740 – 18 June 1798) was an Irish politician. O'Neill was the son of , Member of Parliament for Randalstown, by Catherine Brodrick, daughter of St John Brodrick, of Midleton, County Cork. Lord O'Neill married the Honourable Henrietta Boyle, daughter of , in 1777. He was killed in the Battle of Antrim during the Irish Rebellion of 1798 at the age of 58 and was succeeded in the viscountcy by his son Charles, who was created Earl O'Neill in 1800.