It was one of two titles created on 1 July 1543 for Murrough O'Brien, Prince of Thomond, who claimed descent from Brian Boru, a High King of Ireland.

[1] Following the death of his cousin, Conor Myles John O' Brien in June 2023, Conor John Anthony O' Brien is currently the 19th Baron Inchiquin [2] On his death in 1551, Murrough was succeeded in the earldom, according to the special remainder, by his nephew, the second Earl (see Earl of Thomond for the later history of this title), but the barony of Inchiquin passed to his son Dermod, the second baron.

The fourth earl, also named William O'Brien, represented Windsor, Camelford and Aylesbury in the British House of Commons.

In 1800, he was created Marquess of Thomond in the Peerage of Ireland, with remainder to his brother, the Honorable Edward Dominic O'Brien, a captain in the British Army.

The following year he was made Baron Thomond of Taplow in the County of Buckingham in the Peerage of the United Kingdom to allow him to sit in the House of Lords, with remainder to the male heirs of his body.

He was succeeded in the Irish peerages by his younger brother, James O'Brien, 3rd Marquess of Thomond, an admiral in the Royal Navy.

He was succeeded by his son, Edward O'Brien, 14th Baron Inchiquin, also an Irish Representative Peer and Lord Lieutenant of County Clare.

His son, Lucius O'Brien, 15th Baron Inchiquin, also sat in the House of Lords as an Irish Representative Peer, and also served in the British military and had been appointed High Sheriff of Clare in 1898, and justice of the peace of Salop.