The first of these sieges occurred during the spring of 1642 when Irish Confederate troops besieged and took the town's citadel, King John's Castle from an English Protestant garrison.

About 600 English Protestant settlers had fled to the city to escape the Irish Rebellion of 1641 and had fortified themselves in King John's Castle in the centre of Limerick.

As a result, General Garret Barry, the commander of the Confederate Munster army, marched to Limerick with 1,500 men to secure it.

[3] As he had no siege artillery, Barry put his men to digging mines under the eastern curtain wall and the southeast bastion of the castle,[4] which he intended to collapse by burning their supports.

After five weeks, when the English Protestants were ravaged by disease, they surrendered on terms, before Barry had to collapse his mines and assault the castle.