Lucius William O'Brien, 15th Baron Inchiquin (21 June 1864 – 9 December 1929) was the England-born holder of a hereditary peerage in the Peerage of Ireland, as well as Chief of the Name of O'Brien and Prince of Thomond in the Gaelic Irish nobility.

[2][4][5] Politically a Conservative, O'Brien unsuccessfully stood for the British House of Commons by contesting the Eastern Division of County Clare in 1885.

[6] He succeeded his father's peerage in 1900, serving hence as an Irish Representative Peer in the House of Lords.

In 1921 he was appointed to the Senate of Southern Ireland[4] which was abolished the next year by the formation of the Irish Free State.

Together they had six children:[7] Lord Inchiquin died on 9 December 1929, aged sixty-five, and was succeeded by two of his sons as barons.