Raised as part of the Australian Imperial Force during the First World War, the battalion fought along the Western Front between mid-1916 and late 1918, before being disbanded in early 1919.

Throughout the 1930s, the battalion was merged a couple of times as a result of manpower shortages, but in early 1940, as Australia mobilised for the Second World War, the 49th was expanded and the following year deployed to New Guinea to undertake garrison duty.

Following Japan's entry into the war, the 49th was committed to the fighting in the early stages of the New Guinea campaign, taking part in the Battle of Sanananda in December 1942, where it took many casualties and suffered heavily from disease.

The 49th Battalion was originally formed on 27 February 1916 as part of an expansion of the all-volunteer Australian Imperial Force, which took place after the failed Gallipoli Campaign, during the First World War.

The battalion drew its cadre staff – a total of 14 officers and 500 other ranks – from the 9th, which had been raised primarily from volunteers from the state of Queensland and had been in the thick of the fighting at Gallipoli, having come ashore during the landing at Anzac Cove in the first wave as part of the covering force provided by the 3rd Brigade.

[6] After forming at Tel-el-Kebir, the battalion moved 40 miles (64 km) to the Suez Canal where they undertook a period of training in the desert until early June.

[1] The battalion's first significant action came during the Battle of Mouquet Farm, taking part in two efforts in August and early September.

[9] The 49th Battalion suffered heavy casualties in making their debut – 14 officers and 417 other ranks killed or wounded[10] – and did not take part in any more significant attacks for the rest of the year; nevertheless, they rotated through the front a number of times – firstly around Ypres and then later back in the Somme – where they conducted patrols and raids, in between periods of rest, training and manual labour in the rear.

[1][11] After enduring the harsh winter of 1916–17, early in the new year the Germans withdrew between 15–50 kilometres (9.3–31.1 mi) across a broad front between Arras and the Aisne,[12] as part of a plan to shorten their lines and free up reserves.

On 7 June the 49th joined the Battle of Messines where it advanced on the 13th Brigade's right, past Despagne Farm, into the Blauwepoortbeck Valley where they encountered German pillboxes for the first time.

[17] Further fighting was experienced in late September at Polygon Wood during the Third Battle of Ypres, as part of follow on actions after the success at Menin Road.

[1][18] The Australians wintered in Belgium during which time they undertook mainly defensive actions as they held various positions along the line,[19] but in early 1918 they were moved south to the Somme Valley.

[24] After the German offensive was halted, a brief period of lull during which "Peaceful Penetration" operations were carried out as the Allies sought to regain the initiative.

Consequently, the 49th Battalion was reformed in south-east Queensland within the 1st Military District, headquartered at Kelvin Grove, with company-sized detachments at Toowong, Ipswich and Lowood;[33] it was assigned to the 7th Brigade.

[30] Throughout the initial stages of the war, the Militia battalions were used primarily to provide training for conscripts who were called up for short periods of continuous service once the scheme was re-established in January 1940.

The provisions of the Defence Act prevented them from being sent overseas, though, and the main focus of Australia's combat effort was the all volunteer Second Australian Imperial Force.

[41] At Moresby, the 49th was occupied mainly digging defences and labouring; some training was achieved, although it was largely rudimentary, and a small detachment was also sent to Thursday Island.

[33][48] For the remainder of the month the 49th remained at the front, but their actions were confined mainly to patrolling, providing fire support to neighbouring units and defensive operations.

Sailing upon the transport Duntroon, they disembarked in Cairns and after a period of leave concentrated on the Atherton Tablelands with the rest of the 30th Brigade, which now consisted of the 39th and 3rd/22nd Infantry Battalions.

[50] At this time, the government decided that the 30th Brigade would be converted to an all-AIF unit, and to conduct a period of intense training before sending it back to New Guinea.