1st Brigade is a combined arms formation of the Australian Army. Formed in 1903 as a militia formation based in New South Wales, it was reconstituted as part of the Australian Imperial Force in 1914 for service during World War I, the brigade fought at Gallipoli and on the Western Front before being disbanded in mid-1919. In 1921, the 1st Brigade was re-raised as a unit of Australia's part-time military forces, based in New South Wales. During World War II the brigade undertook defensive duties before being disbanded. In 1948, it was re-raised as an integral part of the Australian Regular Army. Currently the brigade is based at Robertson Barracks in Darwin and at RAAF Base Edinburgh near Adelaide, South Australia. It is the first of the Australian Army brigades to be re-organised as a combat brigade under Plan Beersheba.

The First Australian Imperial Force was the main expeditionary force of the Australian Army during the First World War. It was formed as the Australian Imperial Force (AIF) following Britain's declaration of war on Germany on 15 August 1914, with an initial strength of one infantry division and one light horse brigade. The infantry division subsequently fought at Gallipoli between April and December 1915, with a newly raised second division, as well as three light horse brigades, reinforcing the committed units.