Cadiz was heavily fortified, while the harbour was full of British and Spanish warships. Alburquerque's army and the Voluntarios Distinguidos had been reinforced by 3,000 soldiers who had fled Seville, and a strong Anglo-Portuguese brigade commanded by General William Stewart. Shaken by their experiences, the Spaniards had abandoned their earlier scruples about a British garrison. Victor's French troops camped at the shoreline and tried to bombard the city into surrender. Thanks to British naval supremacy, a naval blockade of the city was impossible. The French bombardment was ineffectual and the confidence of the gaditanos grew and persuaded them that they were heroes. With food abundant and falling in price, the bombardment was hopeless despite both hurricane and epidemic—a storm destroyed many ships in the spring of 1810 and the city was ravaged by yellow fever.

During the siege, which lasted two and a half years, the Cortes of Cádiz – which served as a parliamentary Regency after Ferdinand VII was deposed – drew up a new constitution to reduce the strength of the monarchy, which was eventually revoked by Fernando VII when he returned.