The Battle of Castlebar occurs on August 27, 1798, near the town of Castlebar, County Mayo, during the Irish Rebellion of 1798. A combined force of 2,000 French troops and Irish rebels rout a force of 6,000 British militia in what later becomes known as the “Castlebar Races” or “Races of Castlebar.”

The long-awaited French landing to assist the Irish revolution begun by Theobald Wolfe Tone‘s Society of United Irishmen takes place five days previously on August 22, when almost 1,100 troops under the command of General Jean Joseph Amable Humbert land at Cill Chuimín Strand, County Mayo. The nearby town of Killala is quickly captured after a brief resistance by local yeomen. Following the news of the French landing, Irish volunteers began to trickle into the French camp from all over Mayo.

On August 26, leaving about 200 French regulars behind in Killala to cover his rear and line of withdrawal, Humbert takes a combined force of about 2,000 French and Irish to march on and take Castlebar. In order to avoid a head-on attack, locals advise the French of an alternative route to Castlebar through the wilds along the west of Lough Conn, which the British believe to be impassable for a modern army with attendant artillery train. When General Gerald Lake’s scouts spot the approaching enemy, the surprised British have to hurriedly change the deployment of their entire force to face the threat from this unanticipated direction.

The British have barely completed their new deployment when the Franco-Irish army appears outside the town at about 6:00 AM. The newly sited British artillery opens up on the advancing French and Irish and cut them down in droves. French officers, however, quickly identify an area of scrub and undergrowth in a defile facing the centre of the artillery line which provides some cover from the British line of fire. The French launch a bayonet charge, the ferocity and determination of which unnerve the units stationed behind the artillery. The British units begin to waver before the French reach their lines and eventually turn in panic and flee the battlefield, abandoning the gunners and artillery. A unit of cavalry and British regular infantry attempt to stand and stem the tide of panic but are quickly overwhelmed.

In the headlong flight of thousands of British militias, large quantities of guns and equipment are abandoned, among which is General Lake’s personal luggage. Although not pursued a mile or two beyond Castlebar, the British do not stop until they reach Tuam, with some units fleeing as far as Athlone in the panic. The panic is such that only the arrival of Cornwallis at Athlone prevents further flight across the River Shannon.

Although achieving a decisive victory, the losses of the French and Irish are high, with about 150 men killed, mostly to the cannonade at the start of the battle. About 80 British are killed and some 270 wounded, captured, or deserted. Following the victory, thousands of volunteers flock to join the French who also send a request to France for reinforcements and formally declare a Republic of Connacht, which lasts 3 days and collapses when the French depart.

On September 5, the British forces are again defeated at Collooney however, after that, the rebellion quickly folds. More troops gather and by the Battle of Ballinamuck on September 8, their strength is over 15,000. Ballinamuck is the end for General Humbert, who hands in his surrender. The Irish rebels fight on briefly until scattered. Killala is re-taken on September 12. More French warships sail for Ireland but are decisively defeated by the Royal Navy near Tory Island. With that the 1798 rebellion ends. The captured French soldiers are transferred to England and eventually repatriated. The French officers of Irish origin are hanged in Dublin with the Irish rebels.