Meilyr, Henry's oldest son, succeeded to his father's possessions of Narberth and Pebidiog, the central and north-eastern parts of the modern Pembrokeshire.
[2] Following this campaign, FitzHenry was then part of his uncle Robert FitzStephen's expedition to aid Domnall Mór Ua Briain, King of Thomond.
[2] In 1171, FitzHenry was part of the group of Anglo-Normans that broke the Siege of Dublin by the attacking army led by Ruaidrí Ua Conchobair, King of Connacht.
[2] In 1173, the return of Richard de Clare, 2nd Earl of Pembroke, named Strongbow, to England threw Ireland into revolt.
[2] In October 1175 he accompanied Raymond le Gros in his expedition against Limerick, was second to swim over the River Shannon, and with his cousin David stood the attack of the Irish until the rest of the army had crossed over.
Hugh de Lacy, the next Justice, took away Meilyr's Kildare estate, but gave him Leix in exchange, a marcher district.
In 1182 de Lacy again became Chief Justice, built a castle on Meilyr's Leix estate at Timahoe, and gave him his niece as a wife.
[2] In June 1200 Meilyr was in attendance with King John in Normandy, and on 28 October of that year received a grant of two cantreds in Kerry, and one in Cork.
About the same time he was appointed to Ireland as Lord Chief Justice, the King reserving to himself pleas touching the crown, the mint, and the exchange.
In 1207 FitzHenry was given the land of Offaly by King John, taken from under the lordship of William Marshal, 1st Earl of Pembroke, thereby incurring hatred from the fellow barons of Ireland and head families.
Receiving minor punishment, FitzHenry was allowed to return to Ireland with three letters that summoned to England the officers that were protecting Leinster for William Marshal.
Ultimately, Meiler FitzHenry and his men were captured, their first born sons, or whatever children were available, demanded as a sign of good behavior.
About 1212 his name appears immediately after that of William Marshal, 1st Earl of Pembroke in the protest of the Irish barons against the threatened deposition of John by the Pope, and the declaration of their willingness to live and die for the king.