In 1914, the battalion was the first Australian infantry unit mobilised for service during World War I when it was sent to garrison Thursday Island after fears of possible German military action in the Pacific.

[1] At the same time the 3rd Queensland (Kennedy) Regiment was brought up to an establishment of six companies, one each at Townsville, Ravenshoe and Cairns and three more at Charters Towers collocated with the battalion headquarters.

[4] At the same time Queensland raised a contingent to send to South Africa to contribute to the other Australian colonial forces being sent there to assist the British in fighting against the Boers.

[10][11] In July 1916 the battalion arrived in France where its first involvement of war on the Western Front was the Battle of Fromelles, during which it suffered over 500 casualties and was so badly mauled that it undertook no more offensive action for the rest of the year.

[8] It was here that Private Patrick Joseph Bugden, an original member of the Kennedy Regiment, performed the actions that led to him receiving the Victoria Cross.

[1][4] On 15 May 1918, Sergeant David Emmett Coyne was nominated for the Victoria Cross for throwing himself on a hand-grenade that he had thrown after it had accidentally bounced back off a parapet, in order to protect other soldiers.

[12][13] Later, in August 1918, the 31st Battalion was involved in the last Allied offensive of the war when it took part in the fighting that resulted in the capture of Villers Bretonneux and then Bullecourt.

[1] Upon reforming, the battalion drew personnel from a number of units, including the 31st and 49th Infantry Regiments, the 27th Light Horse, the 21st Australian Army Service Corps Company and the 7th Field Ambulance.

[16] Due to the impact of the Great Depression and a general complacency towards matters relating to defence little was spent on the military during the 1930s and there were only a limited number of volunteers.

[1] Upon the outbreak of World War II in September 1939, the 31st Battalion had subunits based all around northern Queensland including Townsville, Ayr, Home Hill, Bowen, Proserpine, Charters Towers and Ingham.

[18] In 1940 the battalion, along with the other units of the 11th Brigade—then composed of the 26th, 31st and 51st Battalions—was called up for a short period of training as a compulsory military service scheme as part of Australia's mobilisation during World War II and they went into camp near Bowen.

[17] Following Japan's entry into the war in late 1941 the militia were called up on to full-time service and the 11th Brigade began defensive duties in north Queensland.

[1] In early 1943, however, it was decided to release a certain number of men serving in the militia from their compulsory service due to a civilian manpower shortage that was threatening to impact upon the needs of the wartime economy.

[17] For the next ten months until Japan's surrender the 31st/51st Battalion took part in a long and costly campaign and suffered a total of 229 casualties, including 61 killed in action.

[17] Responsible for the northern and central sectors of the island, the battalion initially advanced along the north-east coast, occupying a number of villages, however they did not experience their first action until they crossed the Genga River and attempted to move up the Tsimba Ridge on 17 January 1944, when they came finally in contact with the Japanese.

[17] The Japanese had dug in along the ridge and heavily fortified it with bunkers and mutually supporting machine gun pits and it was only after twenty-one days of continuous fighting that the 31st/51st finally carried the position.

[17] The landing occurred on 7 June, however, the company was quickly surrounded by the Japanese and as the rest of the battalion attempted to break through to them, they were evacuated by sea.

[1][17] They remained there as an occupation force until May 1946 when the unit returned to Australia, where the 31st/51st Battalion (Kennedy and Far North Queensland Regiment) was disbanded on 4 July 1946.