The 1st Light Horse Brigade was a mounted infantry brigade of the Australian Imperial Force (AIF), which served in the Middle Eastern theatre of World War I. The brigade was initially formed as a part-time militia formation in the early 1900s in New South Wales and then later in Queensland. In 1914, the brigade was re-constituted as part of the AIF and was sent to Egypt. Forming part of the New Zealand and Australian Division, during the Gallipoli Campaign it served in a dismounted role between May and December 1915. After being withdrawn to Egypt it served in the Anzac Mounted Division from March 1916 as part of the Egyptian Expeditionary Force, taking part in the Sinai and Palestine Campaign until the end of the war. It was disbanded in 1919. After the war, the AIF light horse regiments were demobilised and disbanded; however, the brigade briefly existed as a part-time militia formation in Queensland until 1921 when its regiments were reorganised into cavalry brigades.

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.