Sir Lucius Henry O'Brien, 3rd Baronet PC (Ire) (2 September 1731 – 15 January 1795) was an Irish baronet and politician for 34 years. He was a man of quite different parts to his father, an intellectual, a Greek and Latin scholar and a brilliant politician. He entered S.C. at Trinity College, Dublin, on 9th. July 1748, at the age of sixteen. He became a B.A. Vernon in 1752. Joined the Irish bar in 1758, and succeeded his father, as 3rd. Baronet of Dromoland, becoming a Privy councillor and M.P.