In 1813, Wellington marched 121,000 troops (53,749 British, 39,608 Spanish, and 27,569 Portuguese) from northern Portugal across the mountains of northern Spain and the Esla River, skirting Jourdan's army of 68,000 strung out between the Douro and the Tagus. Wellington shortened his communications by shifting his base of operations to the northern Spanish coast, and the Anglo-Portuguese forces swept northwards in late May and seized Burgos, outflanking the French army and forcing Joseph Bonaparte into the Zadorra valley.

At the Battle of Vitoria on 21 June, Joseph's 65,000-man army were defeated decisively by Wellington's army of 57,000 British, 16,000 Portuguese and 8,000 Spanish. Wellington split his army into four attacking "columns" and attacked the French defensive position from south, west and north while the last column cut down across the French rear. The French were forced back from their prepared positions, and despite attempts to regroup and hold were driven into a rout. This led to the abandonment of all of the French artillery as well as King Joseph's extensive baggage train and personal belongings. The latter led to many Anglo-Allied soldiers abandoning the pursuit of the fleeing troops, to instead loot the wagons. This delay, along with the French managing to hold the east road out of Vitoria towards Salvatierra, allowed the French to partially recover. The Allies chased the retreating French, reaching the Pyrenees in early July, and began operations against San Sebastian and Pamplona. On 11 July, Soult was given command of all French troops in Spain and in consequence Wellington decided to halt his army to regroup at the Pyrenees.