The 1st Battalion was an infantry battalion of the Australian Army. Although its numerical name was designated during the First World War, the 1st Battalion can trace its lineage back to 1854, when a unit of the Volunteer Rifles was raised in Sydney, New South Wales. This unit has since been redesignated a number of times, but through its links with the units of the colonial NSW defence force, the battalion's history includes services in Sudan and South Africa. During the First World War, the 1st Battalion was raised for overseas service in 1914 as part of the First Australian Imperial Force. Attached to the 1st Brigade, the battalion served in Egypt initially before taking part in the fighting in Gallipoli against the Turks. Later the battalion was sent to the Western Front where it fought in the trenches in France and Belgium as part of the Australian Corps. Following the end of the war the battalion was disbanded in 1919.

In 1921, the battalion was reformed as part of the Militia as the "1st Battalion (East Sydney Regiment)". Throughout the interwar years the unit's designation changed a couple of times and for a time it was amalgamated with the 19th Battalion. During the Second World War the battalion served as garrison force in Australia before being disbanded in 1944 due to manpower shortages. Following the war the 1st Battalion was not re-raised until 1957 when it was reformed as a commando unit in Sydney as the "1st Infantry Battalion (Commando) (City of Sydney's Own Regiment)" before being reduced to a company-sized element in the Pentropic 1st Battalion, Royal New South Wales Regiment. In 1965, the battalion was reformed as the non-Pentropically established "1st Battalion, Royal New South Wales Regiment (Commando)". It maintained the commando role until 1971 when it was amalgamated once again with the 19th Battalion to become the 1st/19th Battalion, Royal New South Wales Regiment, a unit of the Australian Army Reserve that remains in existence today.