The 12th Battalion was among the first infantry units raised for the AIF during the First World War. Half of the battalion was recruited in Tasmania, a quarter was recruited in South Australia, and a quarter from Western Australia. With the 9th, 10th and 11th Battalions it formed the 3rd Brigade.
The battalion was raised within three weeks of the declaration of war in August 1914 and embarked just two months later. After a brief stop in Albany, Western Australia, the battalion proceeded to Egypt, arriving in early December.