The 4th Armoured Brigade was an armoured formation of the Australian Army established during the Second World War. It was formed in February 1943 to provide armoured support for infantry units operating in the South West Pacific Area. Its composition varied over time, but usually comprised several armoured regiments equipped with Matilda II or M3 Grant tanks as well as some support units.

The brigade's main role throughout its existence was to provide a pool of armoured units and sub-units that could be deployed to augment infantry forces. It was also responsible for developing specialised variants of armoured vehicles. Elements of the 4th Armoured Brigade were detached to support most of the Australian Army's major operations from 1943 until the end of the war, and from September 1944 it was the Army's only armoured brigade. The formation was disbanded, after the war, in February 1946.

The 4th Armoured Brigade was established in February 1943 as part of a reorganisation of the Australian Army's armoured units. As there was no longer any threat of Japanese forces invading Australia, the 2nd Armoured Division was disbanded to free up manpower for other purposes. However, it was decided to retain the headquarters of that division's 6th Armoured Brigade to command armoured units that were intended to take part in offensive operations in New Guinea and other locations in the South West Pacific. This specialised formation was designated the 4th Armoured Brigade. The need for armoured support of infantry forces had been demonstrated by the Army's experiences in the New Guinea Campaign during 1942 and early 1943.

The main role of the 4th Armoured Brigade was to provide detachments of tanks to support infantry units. As it was not practical or necessary to deploy large armoured units in the jungle terrain common across the South West Pacific, the brigade was organised into several self-supporting regimental groups. These regimental groups could in turn provide sub-units with the necessary logistics support to form the armoured component of other units during combat operations. This held in practice; during combat deployments regiments from the 4th Armoured Brigade were attached to infantry divisions or brigades, and their squadrons and troops generally operated independently as part of combined arms forces.

Upon formation, the main units of the 4th Armoured Brigade were the 1st Army Tank Battalion, 2/6th Armoured Regiment and 2/9th Armoured Regiment. The 1st Army Tank Battalion was equipped with Matilda II infantry tanks and had previously formed part of the 3rd Army Tank Brigade. The 2/6th Armoured Regiment had formed part of the 1st Armoured Division until August 1942 when it and its M3 Stuart light tanks were transferred to New Guinea. Elements of the regiment saw combat in the Battle of Buna–Gona, where the Stuart tanks were too lightly armoured to be effective. The 2/9th Armoured Regiment was transferred from the 3rd Armoured Division and equipped with M3 Grant medium tanks. The brigade also had several supporting engineer, medical, signals and services units. As the brigade was not intended to operate as a single unit, it lacked the armoured reconnaissance, artillery, combat engineer and infantry units which were standard elements of other Australian Army armoured brigades. The 4th Armoured Brigade's commander from its establishment until its disbandment was Brigadier Denzil Macarthur-Onslow.

The units of the 4th Armoured Brigade were concentrated at Singleton, New South Wales, on 10 March 1943. As of April that year, the brigade formed part of the Land Headquarters Reserve. The 1st Army Tank Battalion was subsequently transferred to Caboolture in southern Queensland and reorganised as a self-supporting battalion group while remaining part of the 4th Armoured Brigade. The unit was redesignated the 1st Tank Battalion on 10 June 1943, and in August that year was shipped to Milne Bay in New Guinea. It subsequently supported the 9th Division during the Landing at Lae and Huon Peninsula campaign. The 1st Tank Battalion returned to Australia in June 1944 and was redesignated again to become the 1st Armoured Regiment. In the meantime the 2/4th Armoured Regiment was added to the 4th Armoured Brigade in October 1943; this unit had previously formed part of the 3rd Armoured Division and was re-equipped with Matilda II tanks. Also in October 1943, a party from the 4th Armoured Brigade armed with pistols was sent to Grovely Camp near Brisbane to put down a riot by soldiers being held under detention there, but did not need to use force. During March 1944 the 2/6th Armoured Regiment was transferred to the 1st Armoured Brigade Group, and the 2/5th Armoured Regiment was transferred from that formation to the 4th Armoured Brigade.

By mid-1944 the 4th Armoured Brigade was located in Southport, Queensland. As of 1 June, the brigade had a strength of 4,719 men and was scheduled to be ready for offensive operations by October that year. During June it also established a training area at Nerang in Queensland, where armoured units could practice operating in tropical conditions. In September 1944 the brigade gained the 2/1st Armoured Brigade Reconnaissance Squadron when the 1st Armoured Brigade Group was disbanded; this unit was reorganised to become the Armoured Squadron (Special Equipment) in January 1945. The 2/6th Armoured Regiment was also reassigned to the 4th Armoured Brigade, but was stationed in the Sydney area. Following the disbandment of the 1st Armoured Brigade Group the 4th Armoured Brigade was the last remaining armoured brigade in the Australian Army.

The 4th Armoured Brigade's structure continued to change during late 1944 and 1945. The 2/1st Armoured Amphibious Squadron was authorised to be raised as part of the brigade in October 1944, but not established until May the next year. This squadron was to operate troop-carrying Landing Vehicles Tracked, but they did not arrive in time for the unit to see action before the end of the war. In January 1945 the 2/6th Armoured Regiment was transferred to the direct control of Land Headquarters, and moved to Puckapunyal in Victoria the next month. This change proved short-lived though, as the 2/6th Armoured Regiment rejoined the 4th Armoured Brigade at Southport during July; B Squadron of this regiment had been transferred to the brigade in April ahead of the remainder of the regiment moving from Victoria to Queensland.