Thomas Fitzmaurice, 18th Baron Kerry

Thomas Fitzmaurice, 18th Baron Kerry and Baron Lixnaw (1574–1630) was an Irish military leader in the Nine Years' War.

He was son of Patrick Fitzmaurice, 17th Baron Kerry, whom he followed into rebellion in 1598. After the death of his father and the capture of Listowel Castle by Sir Charles Wilmot in November 1600, he found himself excluded by name from all pardons offered to the rebels. He went north, and negotiated for aid with Hugh Ó Neill, 2nd Earl of Tyrone and Hugh Roe Ó Donnell. Finding that he was elusive, Queen Elizabeth expressed her willingness that he should be dealt with by pardon of his life only. But by that time he had managed to raise twelve galleys, and felt no inclination to submit.

After the repulse of the northern army from Thomond in November 1601, he was driven to seek safety. In February 1603 an attempt was made to entrap him by Captain Boys, but without success. On 26 October 1603 Sir Richard Boyle noted that he was still operating actively in Munster, but with a small force, and was trying to find pardon from the new king, James I. His application was more than successful, for he obtained a regrant of all the lands possessed by his father. His son and heir, however, was taken away from him and brought up with Donogh O'Brien, 4th Earl of Thomond as a Protestant.

In later life he became involved in disputes. He sat in the Irish parliament of 1615, when a quarrel arose between him and Lords Slane and Courcy over a question of precedency, which was ultimately decided in his favour. He promised his son a jointure on his marriage, but either from inability or unwillingness refused to fulfil his promise. The son complained, and the father was arrested and placed in the Fleet Prison. After a short period of restraint he appears to have agreed to fulfil his contract, and was allowed to return home. Again disdaining to acknowledge the bond, and falling under suspicion of treason, he was rearrested and conveyed to London. He was allowed to return to Ireland, dying at Drogheda on 3 June 1630. He was buried at Cashel, in the chapel and tomb of St. Cormac.

He married, first, Honora, daughter of Connor O'Brien, 3rd Earl of Thomond, by whom he had Patrick, his heir, Gerald, and Joan; secondly, Gyles, daughter of Richard, Lord Power of Curraghmore, by whom he had five sons and three daughters.