After Emperor Napoleon I of France invaded Spain and overthrew the monarchy, Girón offered his services to the patriotic forces in the Peninsular War (also known as the Spanish War of Independence). He participated in the Battle of Bailén in July 1808 where a French corps was annihilated. Later in the year, he fought at the Battle of Tudela in Navarre. In 1809, he served at the Battle of Uclés and in 1811 at the Battle of Albuera. In 1813, the French forces were driven out of Spain after the Battle of Vitoria, which Girón missed because his troops moved in the direction of Bilbao. On 7 October 1813 during the Battle of the Bidassoa, Girón commanded the two Andalusian divisions of Generals Virues and La Torre. Though the Spanish repeatedly attacked the French defenses on Mont Larrun (905 meters alt.), they failed to capture the position. The Marquess of Wellington praised his allies' performance, writing that the Spanish attacked, in as good order and with as much spirit as any that I have seen made by any troops. The French abandoned the peak the next day to avoid being trapped. Girón also led the two divisions, with 7,653 soldiers in all, at the Battle of Nivelle on 10 November, where his troops helped take the fortified village of Sare.