Ely O’Carroll was granted to FitzWalter by Henry II., nevertheless King John re-granted it to William de Braosa in 1200, and FitzWalter had to buy it back to regain possession.
It shortly afterwards passed into the hands of Hugh de Hose or Hussey.
The English rebuilt and enlarged the stronghold in 1213.
In 1432 the Earl of Ormond went to war with O’Carroll of Ely, and demolished his two chief castles, which most likely were Birr and Leap, for in spite of Royal grants the stronghold remained in the possession of the O’Carrolls.
A dispute arose about the chieftainship of the sept in 1532, the senior branch of the family holding Birr Castle.
Ferganainm O’Carroll, the son of the late chief, enlisted the aid of the Earl of Kildare, whose daughter he had married, and together they laid siege to Birr. The Earl received a bullet in his side from the garrison. It is said that a soldier, hearing him cry out in agony, remonstrated with him, remarking he himself had been wounded three times and was none the worse, to which the Earl replied he was sorry he had not received the fourth bullet in his stead. The ball was extracted the following spring, but it is said to have hastened his end.
In 1537 Lord Leonard Grey took Birr Castle, and is reported to have received submission from O’Carroll, who was created Baron of Ely in 1552.
At the time of the plantation of Ely, Birr and its castle were granted to Sir Laurence Parsons in 1620, and the same year his steward arrived to make preparations. Shortly afterwards O’Carroll appealed in vain.
In 1641 Sir William Parsons was made Governor of Ely O’Carroll and the Castle of Birr, which latter he garrisoned with his tenants.
He put the place at once in a state of defence. He raised a flanker behind the stables, and erected scaffolds inside the castle for the garrison to fight from.