During World War I, the 19th Battalion was raised as a unit of the Australian Imperial Force, attached to the 5th Brigade, of the 2nd Division.

The unit was formed in 1915 and was first sent to Gallipoli where it fought against the Turks, before being withdrawn from the peninsula and being sent to France in early 1916, where it served in the trenches along the Western Front.

[4] In 1903, following the Federation of Australia, this unit became part of the Commonwealth Military Forces and was subsumed into the 1st Australian Infantry Regiment.

As a part of this, the 19th Battalion was raised in March 1915, in Liverpool, New South Wales, drawing some of its personnel from men who had already served with the Australian Naval and Military Expeditionary Force.

Later, the battalion was sent to Anzac Cove as part of a wave of reinforcements that were sent to the peninsula following the initial landing,[8] arriving there on 21 August 1915.

[7] Following that, it took part in the attack on Battle of Hill 60,[7] during which it was dispatched to the Azmak Dere, where a gap had formed following the British 11th Division's withdrawal amidst confused fighting.

In November 1916, following a period of respite in a quieter sector in Belgium, the 19th Battalion involved in an attack on a trench system known as "the Maze" near Flers, suffered devastating losses in winter conditions that were described as the "worst ever encountered by the AIF".

[7] In 1918 the battalion helped to repel the German spring offensive, and it was during this time, on 7 April 1918, that Lieutenant Percy Storkey earned a Victoria Cross for his actions during the fighting in Hangard Wood.

[7] Following this, the battalion took part in the Allied offensive that eventually brought about the end of the war, fighting around Amiens and Mont St Quentin before coming up against the "Beaurevoir Line" at Estrees on 3–4 October 1918.

This engagement was the battalion's last combat operation in the war, as the whole of 2nd Division was withdrawn from the line after the 6th Brigade's attack on Montbrehain on 5–6 October.

There are 874 names of 19th Battalion personnel killed in action recorded on the Australian War Memorial (AWM) Roll of Honour.

[5] In April 1921, following a review of Australia's defence requirements as the demobilisation process came to an end, the AIF was officially disbanded and the decision was made to reorganise the units of the Citizens Forces to perpetuate the designations and battle honours of the AIF battalions;[3][14] this saw the multi-battalion regiments disbanded and single battalions being formed.

[24] After their relief, the 19th was transported to Mt Isa and then flown back to Narellan where the troops were given a long period of leave.

In July it deployed to the Buna area in New Guinea where it was used on defensive duties carrying out patrols and providing labour for work parties.

[27] In December 1944, the battalion was sent to New Britain, embarking upon the transport Francis J. Parkman,[28] and over the course of the next five months they undertook a campaign of harassment operations to keep the large number of Japanese forces stationed there off balance.

[32] On 5 March, the 19th attempted to cross the river, but was initially turned back by intense Japanese mortar and machine-gun fire.