During the civil war he commanded the Harriers Column that left Barcelona to fight in front of Huesca. García Vivancos agreed with the militarization of the militias and tried to cooperate with the communists. Later he commanded the 125th Mixed Brigade and the 25th Division, intervening in the battles of Belchite and Teruel. In May 1938 he was promoted to the rank of lieutenant colonel. During the rest of the war, he also held command of the 29th Division - a former POUM militia - and the 24th Division — replacing the fugitive Antonio Ortiz Ramírez.