O'Neill escaped with some of his troops, but although the Irish Confederate Wars continued until 1653, Clonmel ended effective Royalist resistance in Ireland,[a] and Cromwell returned to England immediately afterwards.

Ormond arrived in person at the end of the month and the Clare men were replaced by experienced soldiers from Ulster under O'Neill, a veteran of siege warfare in the Thirty Years' War.

In answeare whereunto I thinke fitt to assure you by these that rather then that towne should fall into the hands of the rebels I shall draw all the forces of the Kingdome into a body for its reliefe which I shall endeavour soe to effect as in ten dayes to be in a readiness to advance to towards you, relying on your uttermost endeavours to defend that place during that tyme though you should as you expect be closely besieged and soe deseiring to heare as frequently from you as possibly you may.

It was intended that his infantry would storm this breach and then open the nearby North town gate to allow access to Cromwell and the Parliamentarian cavalry.

[b] However, O'Neill put all able-bodied townspeople to work building a coupure inside the breach lined with artillery, muskets, and pikemen.

The Parliamentarian infantry which assaulted the breach was engaged by pikemen and repeatedly cut down by marksmen on the earthworks behind until the soldiers finally refused to make any further attacks on what was a death trap.

[c]Cromwell was with a second assault force waiting for the town North (or Lough) gate to be opened by the party that had stormed the breach.

[5] Cromwell knew that O'Neill's garrison and supplies were severely depleted and planned the next morning to try a fresh assault with close artillery support to batter the coupure and its defenders.

Although he was angry, Cromwell made his men abide by the terms of the surrender agreement and treat the townspeople and their property with respect.

Commandinge therefore both horse and foot pell mell that such a heape in such an occasion was seldome scene that by the very thronge severall of them perished, advancinge forwarde unawares (both opposition and assaulte being soe furious and hott) not observinge either ditche or counterscarfe fell headlonge into the said ditche from whence there was no redemption or possibilitie of recoverie but there were massacred and butchered.