Meiler Fitzhenry was the son of Henry, the natural son of King Henry 1 by Nesta ap Rhys, daughter of Rhys ap Tewdwr, prince of South Wales. In 1157, Meiler succeeded to his father’s possessions in the central and northeastern parts of modern Pembrokeshire. In 1169, he accompanied his uncle Robert fitzStephen to Ireland where he established his reputation as one of the premier knights. FitzHenry was appointed chief governor of Ireland by Richard I, and his position was later reaffirmed by King John who in 1204 ordered him to build a castle in Dublin to serve as a court and treasury. During his justiciarship Meiler clashed with both the clergy and his fellow barons. William de Braose was the first of the magnates to clash with Meiler, a dispute that John solved in 1200 by recalling Meiler to court to accompany him on circuit in England and in Normandy. In 1201 and 1202, vacancies arose in the bishoprics of Armagh and Tuam and, at Meiler’s prompting, an illegal election was held that recommended colonists for the positions. Early in 1203, William de Burgh, constable of Limerick City, set out for Connacht to unseat Cathal Crobderg Ua Conchobair, who, unwilling to challenge de Burgh on the field, was saved by the intervention of the justiciar. As a result of de Burgh’s expulsion, de Braose was appointed in July of that year to succeed him as constable of Limerick. William almost at once transferred the lucrative post to his son-in-law Walter de Lacy. Shortly afterward John ordered de Lacy to surrender Limerick to the justiciar, but this action did not meet with the approval of the de Lacy-de Braose axis and subsequently disturbances broke out in Meath.
Concurrently a conflict was in progress with John de Courcy, lord of Ulster. De Courcy was eventually overthrown and in 1205 Hugh de Lacy was installed as earl of Ulster. Meiler’s most serious adversary was William Marshal, with whom he was in dispute over land. Meiler was a tenant-in-chief of two fiefs in Kerry and Cork, granted to him by John around the time he was confirmed as justiciar. The bulk of his lands were held by the Marshal in his capacity as lord of Leinster. A long-running dispute followed; eventually, in 1208, John summoned both opponents and several other barons of Leinster to discuss the friction in his lordship. However, while both were in London, Meiler’s forces were defeated by an opposition reinforced by his previous ally, Hugh de Lacy; no longer a tenable power, he was replaced as justiciar. FitzHenry remained a powerful baron even after he ceased to be justiciar. Married to a niece of Hugh de Lacy, he had one son whom he outlived. When Meiler died in 1220 he was interred in the Augustinian monastery of Great Connell that he had founded in 1202. His grave is marked by perhaps the earliest example of an Anglo-Norman headstone in Ireland, bearing this inscription: "Conduntur tumulo Meyleri Nobilis ossa, Indomitus domitor totius gentis Hiberniae."