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.

Originally formed in 1903 as a Militia unit of the Commonwealth Military Forces, it was established in New South Wales and consisted of four battalion-sized units—1st, 2nd, 3rd and 4th Australian Infantry Regiments.

[3] In 1912, the compulsory training scheme was introduced and at this time, the brigade was reorganised as part of the 1st Military District, with constituent units were spread across various locations in Queensland including Townsville, Cairns, Charters Towers, Mackay, Rockhampton, Mount Morgan, Bundaberg, Maryborough, Gympie, and Brisbane.

[4] The 1st Brigade was re-constituted in Sydney, shortly after the start of World War I in August 1914 for service overseas as part of the Australian Imperial Force (AIF).

There, it was brought back up to strength and in mid-1916 the brigade was transferred to Europe, where it took part in the fighting on the Western Front in France and Belgium between 1916 and 1918,[5] before being disbanded in April 1919.

[8] Notable battles in which the brigade fought include: Lone Pine, Pozières, Bullecourt, Passchendaele, Hazebrouck, Amiens and the Hindenburg Line.

As a result, the Army's budget was halved and the scope of the compulsory training scheme was scaled back; with this the authorised strength of each infantry battalion was reduced to just 409 men of all ranks.

[14] In 1929, the compulsory training scheme was suspended by the newly elected Scullin Labor government and was replaced by a voluntary system,[15] under the new name of the "Militia".

Although some Militia units were committed to combat operations in New Guinea from 1942 onwards, the 1st Brigade remained in Australia for the duration of the war, headquartered around Parramatta, New South Wales,[19] where it formed part of the 1st Division.

[28] In late 1964, however, the decision was made to end the experiment with the Pentropic establishment,[29] partly because of the difficulties it created with allied interoperability.

Shortly after this, the 1st Task Force, consisting of the 5th Battalion, Royal Australian Regiment (5 RAR), undertook a readiness exercise around Gospers in New South Wales.

This saw the 5th/7th Battalion, Royal Australian Regiment (5/7 RAR), re-equipped with armoured personnel carriers, which they began to receive in July 1983.

[37] In 1992, the brigade began the process of moving to Darwin as part of a force structure review focused upon relocating defence assets in the north.