The Canadian government declared its neutrality on the outbreak of the Spanish Civil War. Most people in Canada favoured neutrality but some men joined the International Brigades. About a 1,000 Canadian citizens joined the defence of the Popular Front government.

The Mackenzie-Papineau Battalion was established in July 1937. It was named after two nineteenth-century leaders in Canada's independence movement. The soldiers who fought in the unit mainly came from Canada but did include Canadian immigrants living in the United States. When the Mackenzie-Papineau Battalion arrived in Spain it was incorporated into the Abraham Lincoln Battalion.

The battalion first saw action at Fuentes de Ebro on 13th October 1937. In this offensive 60 were killed and 200 were wounded. The Mackenzie-Papineau Battalion also took part in the battles at Teruel (December 1937) and Ebro (July-August 1938). By the end of the Spanish Civil War almost half of the Canadian volunteers had been killed.