Cromwell arrives at Wexford on the 2nd of October 1649 with about six thousand men, eight heavy siege guns and two mortars.
He concentrates his force on the 6th of October on the heights overlooking the southern end of the town.
The town's garrison initially consists of fifteen hundred Confederate soldiers under David Sinnot.
However, the morale of the town is low—perhaps as a result of hearing the fall of Drogheda on September 11—and many of the civilians in Wexford want to surrender.
Sinnot, however, appears to have strung out surrender negotiations with Cromwell and has been steadily reinforced, bringing his garrison strength up to forty-eight hundred men by the 11th of October.
In addition, the main Royalist/Confederate force under James Butler, 1st Duke of Ormonde, is close by at New Ross.
Sinnot insists on several conditions for surrender that Cromwell will not countenance, including the free practice of the Catholic religion, the evacuation of the garrison with their arms and the free passage of the privateer fleet to a friendly port.
Negotiations are reopened when Cromwell's guns blast two breaches in the walls of Wexford castle, opening the prospect of an assault on the town.
However, while negotiations are still proceeding, Stafford, the English Royalist captain of Wexford Castle (part of the town's defenses), surrenders the castle, for reasons that have never been determined.
The troops of the New Model Army, on their own initiative, immediately assault the walls of the town, causing the Confederate troops to flee in panic from their positions.
The Parliamentarians pursue them into the streets of Wexford, killing many of the town's defenders.
Several hundred, including David Sinnot, the town governor, are shot or drowned as they try to cross the river Slaney.
Estimates of the death toll vary. (Cromwell himself thought that over two thousand of the town's defenders had been killed compared with only twenty of his troops.)
Several Catholic priests, including seven Franciscans, are killed by the Roundheads.
Much of the town, including its harbor, is burned and looted.
As many as fifteen hundred civilians are also killed in the sacking. (This figure is difficult to corroborate but most historians accept that many civilians were killed in the chaos surrounding the fall of Wexford.)
The destruction of Wexford is so severe that it cannot be used either as a port or as winter quarters for the Parliamentarian forces.
One Parliamentarian source therefore describes the sack as "incommodious to ourselves".
Cromwell reports that the remaining civilians had "run off" and asked for soldiers to be sent from England to repopulate the town and reopen its port.
