A predecessor 129th Mixed Brigade had been established in 1937 made up mainly of POUM militiamen. It was made part of the new 29th Division of the Spanish Republican Army and saw its baptism of fire in Northern Aragon. Owing to its alleged faulty performance in the combats of the Battle of Sabiñánigo and the Huesca Offensive, both the brigade and the division were wrapped up. The disbandment, however, fell in line with the persecution of the POUM by the Communists following the May Events of 1937 in Barcelona.