The Battle of Ballyellis, a clash during the Irish Rebellion of 1798, takes place on June 30, 1798. The battle is between a surviving column of the dispersed Wexford rebel army and pursuing British forces. It is the last Irish victory in the most violent Irish rebellion in modern history with at least 10,000 killed in a campaign that sees appalling atrocities inflicted by English and Irish.

The British victory at the Battle of Vinegar Hill on June 21 had denied the rebels static bases of operation but had not finished the rebellion and at least three major columns of rebels are operating throughout the southeast, moving outwards from County Wexford in an effort to spread and revive the rebellion.

One such column, numbering about 1,000 but accompanied by a number of women and juveniles, is mobile in north County Wexford, continually altering course to elude combined movements of pursuing British forces. The column is led by Joseph Holt, and under his command Denis Taaffe. It heads in the direction of Carnew, County Wicklow, toward the security offered by its mountain ranges when one of its foraging parties is intercepted and destroyed by a cavalry patrol. It quickly becomes evident to the British authorities that this party is a detachment from the main body of rebels. A mounted force of 200 troops consisting of Ancient Britons, dragoons, and three yeomanry corps, assemble near the neighbourhood of Monaseed to begin a pursuit of the rebels.

However, the approaching British are spotted and a force of rebels then moves ahead of the main force to prepare an ambush at the townland of Ballyellis. The spot chosen is behind a curve in the road flanked by high ditches and estate walls. Wagons are placed on the road and access points cut into the ditches. The main force arrives and deploys itself behind the wagons, on the wall and ditches with a small force left to stand on the road ahead of the barricades standing to face and lure in the approaching soldiers.

Upon spotting the small force standing on the road, the pursuing British quicken their pace and charge forward, assuming that they are facing only the rearguard of the fleeing column. Upon reaching the turn, they are met by a barrage of gunfire and are hemmed in by the rebels on three sides. As more mounted troops arrive they press their comrades further into the trap making effective manoeuvre impossible and many are easily picked off by the long pikes of the rebels.

The rear-ranks quickly flee with a few more soldiers escaping by jumping their mounts over the ditch. The rebels organise a relentless pursuit of the soldiers who are tracked and killed through the adjoining fields. At the end of the action about 120 troops, including a French émigré, and two officers are killed with no rebel casualties.

The news of this rebel victory comes as a shock to the authorities in Dublin Castle who had assumed that the offensive capabilities of the rebels had been finished at the Battle of Vinegar Hill. Reports of the defeat are downplayed and the scale of losses withheld from the general public, but the military now recognises Wicklow as the main theatre of rebel operations and begins to transfer troops there in anticipation of a new anti-insurgency campaign.