Maquis activity in Spain had its heyday towards 1946, after which the resistance fighters were heavily repressed during the Trienio del Terror (1947–1949), which included such instances of White Terror as paseos and applications of the Ley de fugas (extralegal executions predicated on detainees' actual or supposed attempts to escape custody) taking a heavy toll among maquis combatants and their supporters.

Referring to the contribution of the Spanish Maquis to the French resistance movement, Martha Gellhorn wrote in The Undefeated (1945): During the German occupation of France, the Spanish Maquis engineered more than four hundred railway sabotages, destroyed fifty-eight locomotives, dynamited thirty-five railway bridges, cut one hundred and fifty telephone lines, attacked twenty factories, destroying some factories totally, and sabotaged fifteen coal mines.

[6] In October 1944 a group of 6,000 maquis including Antonio Téllez Solà invaded Spain via the Aran Valley but were driven back after ten days.

Few details of the maquis' actions in Spain have been made public because of the secrecy of the Franco government, but guerrillas, including Francesc Sabaté Llopart, Jose Castro Veiga, and Ramon Vila Capdevila were responsible for the deaths of hundreds of Guardia Civil (Civil Guard) officers, and uncountable acts of industrial sabotage.

Despite the failure of the invasion of the Val d'Arán that year, some columns continued to progress into the Spanish interior and to connect with the groups that had remained in the mountains since 1939.

Hundreds of thousands of Republican soldiers and civilians crossed the French border ahead of the advancing Nationalist troops in Catalonia.

There were 22 camps in total: Barcarès, Agde, Saint-Cyprien, Argelès-sur-Mer, Berck-Plage, Montpellier Chapallete, Fort Mahon Plage, Tour de Carol, Septfonds, Baste-les-Foages, Bram, Haros, Gurs, Vernet d'Ariège, Rivesaltes, Fort Colliure, and Rieucros in Metropolitan France and, in French North Africa, Camp Morand, Meridja, Djelfa, Hadjerat-OM'Guil, and Ain-el-Curak.

On 11 October 1940 the Vichy regime started the Companies of Foreign Workers (Compagnies de Travailleurs Etrangers, CTE), which permitted prisoners to leave the concentration camps, if they would go to work in factories.

In April 1942 a meeting of several Spanish combat groups decided to take the name of the XIV Cuerpo del Ejército de Guerrilleros Españoles, considering themselves the Corps' successors.

This conveyed the group's distancing from the Francs-Tireurs et Partisans (FTP), the armed branch of the French Communist Party, with whom they had previously worked closely.

By this time, the Spanish resistors had participated in numerous armed actions against the German army, even liberating various populations in the south of France.

The most notable operation of the Spanish maquis was the invasion of Spain by between 4,000[12][13] and 7,000[11] guerrillas through Val d'Aran and other parts of the Pyrenees, well equipped and with heavy weapons, on October 19, 1944, after the German Army had been driven from the south of France.

[14] The objective of the offensive was to retake the sector of Spanish territory comprising the land between the Cinca and Segre Rivers and the French border.

Later, the zone was declared conquered by the Spanish Republican government in exile, with the intention of provoking a general uprising against Franco throughout Spain.

[15] The guerrilla army conquered various towns and villages, raising the Spanish Republican flag, carrying out anti-Franco meetings in the plazas, as well as controlling part of the French border for several days, through which they were able to bring in trucks, material and reinforcements from France.

[16] In spite of the setback of Arán in 1944, the expectations of the exiled Spanish Communist Party (PCE) remained high, given that all seemed still possible in an international context of general collapse of fascism.

All throughout Spain, the level of guerrilla activity went up, precipitated by the incorporation of new contingents forced to cross the border from France[16] and the reorganization of the groups with structures of a more military character.

People in these groups who wanted to leave and rejoin a normal civilian life were most of the time treated as deserters and shot,[16] even at the rearguard guerrilla camps in France.

On the rare occasion that an item appeared in the press, the maquis were always referred to as "bandoleros" (bandits), in order to strip the actions of all political context.

Most of their members were middle-aged or older by 1950, with the consequent detriment of their physical capacities accelerated by years of living exposed to the elements and the lack of proper medical and food supplies.

Of those who stayed in Spain, some were sentenced only to jail (some spent up to 20 years in prison), some were judged summarily and shot, and others died at the hands of the Guardia Civil through application of the Ley de Fugas ("law of fugitives").

The end was marked by the shooting deaths of Francisco Sabate Llopart (El Quico) in 1960, and Ramon Vila "Caracremada" in 1963, both in Catalonia, and José Castro Veiga [es] in Galicia in March 1965.

In areas of harsher weather, like in the mountains of León, the maquis would relatively often pass periods of time more or less "undercover", in small groups, in support houses in villages, especially during the winter months.

In effect, given the silence of the press and government on the situation, very few and scattered inhabitants of areas of maqui activity were actually aware of the conflict.

There were others called "passive militias", and "guerrilleros del llano" ("guerrillas of the plains"), who supplied aid, from food to armaments when necessary, as well as information.