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.
After some skirmishing the fortress was closely besieged in 1642, and of the nine hundred people in town and castle many died of starvation, while others were reduced to eating dogs and cats.
At length the Earl of Ormond sent a detachment to its relief, but early the next year General Preston approached the stronghold with artillery and troops.
He reconnoitred the town from Drumbawn Hill, and after firing a few shots encamped in the neighbouring woods. On the second day of the siege he sent a messenger to the Governor to inquire if he held the castle for the King or the Parliament, and asking to be allowed to garrison it for his Majesty’s use.