Its first significant action came during the Battle of Messines in June 1917, as part of the successful, but costly, effort to capture the Wytschaete–Messines Ridge near the salient that had developed in the frontline around Ypres.

[9] During the fighting around Broodseinde, the 43rd formed part of the 3rd Division's spearhead and was successful in helping them advance over 2,000 yards (1,800 m), while during the attack on Passchendaele the battalion formed part of the divisional reserve along with the rest of the 11th Brigade and was committed to the front line late after the assaulting forces were forced to retire after their initial gains were negated by German attacks on the division's flank.

With the vital rail head of Amiens threatened, the Australian units which had wintered in Belgium were brought south to the Somme to help stem the tide of the German advance.

[12] After the German offensive was halted, as the Allies sought to regain the initiative, they took part in the Battle of Hamel in July,[3] where the battalion attacked in the centre of the 11th Brigade, tasked with securing the village itself.

For his actions during this battle Corporal Lawrence Weathers was awarded the Victoria Cross, the only member of the 43rd Battalion to be bestowed this honour, receiving it for attacking two German trenches with grenades during an assault on the Bouchavesnes Ridge on 2 September 1918.

[14] In early October 1918, the Australian Corps, which had suffered heavily during the fighting earlier in the year, was withdrawn from the line for rest and reorganisation and did not return to the front before the armistice was signed in November.

[16] Although it currently no longer exists, for a period after 1966, following the reintroduction of national service, the 43rd Battalion was re-raised within the RSAR, as a remote area battalion within the Citizens Military Force, offering special conditions of service for soldiers who had elected to serve in the CMF rather than the Regular Army, but who could not meet their training requirements through normal attendance due to their occupation or place of residence.