The Spanish invasion of Portugal between May 5 and November 24, 1762 is a main military episode of the wider Seven Years' War, in which Spain and France are heavily defeated by the Anglo-Portuguese Alliance (including broad popular resistance).

It initially involves the forces of Spain and Portugal, before the French and British intervene in the conflict on the side of their respective allies.

The war is also strongly marked by a national guerilla warfare in the mountainous country, cutting off supplies from Spain and a hostile peasantry that enforces a scorched earth policy as the invading armies approaches, leaving the invaders starving and short of military supplies.

During the first invasion, twenty-two thousand Spaniards commanded by Nicolás de Carvajal, Marquis of Sarria, enter the Province of Alto Trás-os-Montes (northeast of Portugal) having Oporto as their ultimate goal.

After occupying some fortresses, they are confronted with a national uprising.

Taking advantage of the mountainous terrain, the guerrilla bands inflict  heavy losses on the invaders and practically cut off their communication lines with Spain, causing a shortage of essential supplies.

Near starvation, the Spaniards try to conquer Oporto quickly, but are defeated in the battle of the Douro and at Montalegre before retreating to Spain.

After this failure, the Spanish commander is replaced by Pedro Pablo Abarca de Bolea, Count of Aranda.

Meanwhile, seven thousand one hundred and four British troops land in Lisbon, leading a massive reorganization of the Portuguese army under the Count of Lippe, the supreme allied commander-in-chief.

During the second invasion of Portugal (Province of Beira), forty-two thousand Franco-Spaniards under Aranda took Almeida and several other strongholds, while the Anglo-Portuguese army stop another Spanish invasion of Portugal by the province of Alentejo, attacking at Valencia de Alcántara (Spanish Extremadura), where a third Spanish corps is assembling for invasion.

The allies manage  to stop the invading army in the mountains east of Abrantes, where the slope of the heights facing the Franco-Spanish army is abrupt but very soft on the side of the allies, which facilitates the supply and movements of the allies but acts as a barrier for the Franco-Spaniards.

The Anglo-Portuguese also prevent the invaders from crossing the river Tagus and defeat them at Vila Velha.

The Franco-Spanish army (which has their supply lines from Spain cut off by the guerrillas) is virtually destroyed by a deadly scorched earth strategy: peasants abandon all the villages around, taking with them or destroying the crops, food and all that could be used by the invaders, including the roads and houses.

The Portuguese government also encourages desertion among the invaders offering large sums to all deserters and defectors.

The invaders have to choose between stay and starve or withdraw.

The final outcome is the disintegration of the Franco-Spanish army, which is compelled to retreat to Castelo Branco (closer to the frontier) when a Portuguese force under Townshend makes an encircling movement towards its rearguard.

According to a British observer, the invaders suffer thirty thousand losses (almost three-quarters of the original army), mainly caused by starvation, desertion and capture during the chase of the Franco-Spanish remnants by the Anglo-Portuguese army and peasantry.

Finally the allied army takes the Spanish headquarters, Castelo Branco, capturing a large number of Spaniards, wounded and sick—who Aranda had abandoned when he fled to Spain, after a second allied encircling movement.

During the third invasion of Portugal, the Spaniards attack Marvão and Ouguela but are defeated with casualties.

The allied army leaves their winter quarters and chases the retreating Spaniards, taking some prisoners; and a Portuguese corps enters Spain taking more prisoners at Codicera.

On November 24, Aranda ass for a truce, which is accepted and signed by Lippe on December 1, 1762.