During World War II, the battalion served in a garrison role in Australia and was disbanded in 1944 without having seen active service overseas.

[3] Following training, the battalion was sent to Egypt, and from there to Gallipoli in August 1915 as part of a wave of reinforcements that arrived after the initial landing.

[3] After returning to Egypt, the AIF underwent a period of reorganisation as it was expanded from two infantry divisions to five prior to their transfer to Europe.

In May, the 18th Battalion was committed to the Second Battle of Bullecourt before moving again to Belgium where they saw further action around the Ypres Salient at Menin Road in September and Poelcappelle in October before settling down for the winter.

With the Germans making rapid gains, Australian units, including the 18th Battalion, were moved south from Belgium where they had spent the winter and they were thrown into the line to help blunt the attack around Villers-Bretonneux, which lay before the strategically important rail hub at Amiens.

There, at Montbrehain, on 3 October 1918, Lieutenant Joseph Maxwell earned the battalion's first and only Victoria Cross in what was ultimately to prove their last engagement of the war.

[14] Australia's part-time military force was re-organised in 1921 to perpetuate the numerical designations, battle honours and formations of the AIF.

[15] The 18th Battalion was re-raised in the Kuring-Gai region of Sydney, as part of the Citizens Forces, at this time drawing personnel from 17th and 18th Infantry Regiments.

[18] At the outbreak of World War II, the battalion was based at Willoughby, New South Wales, where it formed part of the 8th Brigade, attached to the 1st Division within the 2nd Military District.