The first head of the unit was the militia major Victoriano Castán Guillén, while Saturnino Carod Lerín of the CNT was appointed as political commissioner.

In December 1937 the 118th MB was sent to the Teruel Front, taking part in the capture of the city; it fought in the Old Cemetery and in the Hermitage of Santa Bárbara, reaching the vicinity of the urban area.

The old cemetery was occupied by the brigade on December 21, and two days later it took the Hermitage of Santa Bárbara and the position of "El Mansueto."

On January 1, 1938, it managed to stop an enemy counteroffensive that threatened to break the republican siege on Teruel, although it suffered a high number of casualties.

It still had the strength to go to reestablish the front threatened by the national troops who were trying to lift the siege, although the brigade came out of the fight very broken.