Charles invaded Guyenne with three separate armies, all headed for Bordeaux. Talbot received 3,000 additional men, reinforcements led by his fourth and favourite son, John, the Viscount Lisle. The French laid siege to Castillon (approximately 40 kilometres (25 mi) east of Bordeaux) on 8 July. Talbot acceded to the pleas of the town leaders, abandoning his original plan to wait at Bordeaux for more reinforcements, and set out to relieve the garrison.

The French army was commanded by committee; Charles VII's ordnance officer Jean Bureau laid out the camp to maximize French artillery strength. In a defensive setup, Bureau's forces built an artillery park out of range from Castillon's guns. According to Desmond Seward, the park "consisted of a deep trench with a wall of earth behind it which was strengthened by tree-trunks; its most remarkable feature was the irregular, wavy line of the ditch and earthwork, which enabled the guns to enfilade any attackers". The park included up to 300 guns of various sizes, and was protected by a ditch and palisade on three sides and a steep bank of the River Lidoire on the fourth.

Talbot left Bordeaux on 16 July. He outdistanced a majority of his forces, arriving at Libourne by sunset with only 500 men-at-arms and 800 mounted archers. The following day, this force defeated a small French detachment of archers stationed at a priory near Castillon. Along with the morale boost of victory at the priory, Talbot also pushed forward because of reports that the French were retreating. However, the cloud of dust leaving the camp which the townsmen indicated as a retreat was in fact created by camp followers departing before the battle.

The English advanced but soon ran into the full force of the French army. Despite being outnumbered and in a vulnerable position, Talbot ordered his men to continue fighting. The battle ended in an English rout, and both Talbot and his son were killed. There is some debate over the circumstances of Talbot's death, but it appears that his horse was killed by a cannon shot, and its mass pinning him down, a French archer in turn killed him with an axe. With Talbot's death, English authority in Gascony eroded and the French retook Bordeaux on 19 October. It was not apparent to either side that the period of conflict was over. In hindsight, the battle marks a decisive turning point in history, and is cited as the endpoint of the period known as the Hundred Years' War.