The 24th Battalion was an infantry battalion of the Australian Army. Originally raised in 1915 for service during World War I as part of the 1st Australian Imperial Force, it was attached to the 6th Brigade, 2nd Division and served during the Gallipoli campaign and in the trenches of the Western Front in France and Belgium. Following the end of the war the battalion was disbanded in 1919, however, in 1921 it was re-raised as a unit of the part-time Citizens Forces in Melbourne, Victoria. In 1927, when the part-time forces adopted territorial titles, the battalion adopted the designation of 24th Battalion (Kooyong Regiment). In 1939, the 24th Battalion was merged with the 39th Battalion, however, they were split up in 1941 and in 1943, after being allocated to the 15th Brigade, the 24th Battalion was deployed to New Guinea before later taking part in the Bougainville campaign. Following the end of the war, the battalion was disbanded in 1946.

The 24th Battalion was raised in May 1915 at Broadmeadows Camp in Victoria, as a unit of the all-volunteer Australian Imperial Force (AIF). Along with the 21st, 22nd and 23rd Battalion, the 24th formed part of the 6th Brigade, which was assigned to the 2nd Division. It had originally been planned that the battalion would be raised from personnel drawn from outside of Victoria and it was designated as an "outer states" battalion meaning that it would draw its recruits from the less populous states of Queensland, Tasmania, South Australia and Western Australia; however, due to the large number of recruits that had arrived at Broadmeadows at the time it was decided to raise the battalion there, from Victorian volunteers. As a result of the hasty decision to raise the battalion very little training was carried out before the battalion sailed from Melbourne just a week after being formed.

Organised into four rifle companies, designated 'A' through to 'D', with a machine gun section in support, the battalion had an authorised strength of 1,023 men of all ranks. After arriving in Egypt, the 24th completed its training during July and August before being sent to Gallipoli in early September as reinforcements for the forces that had landed there in April. Arriving on the peninsula on 4 September, the 24th served in the Lone Pine sector, taking over responsibility for the front line on the 12 September. The position was very close to the Turkish trenches and was hotly contested. The position was so tenuous, that the troops holding it had to be rotated regularly, and as a result the 24th spent the remainder of the campaign rotating with the 23rd Battalion to hold the position against determined Turkish mining operations. The battalion remained at Gallipoli for three months until the evacuation of Allied troops took place in December 1915. During the period that the 24th was deployed to Gallipoli, a 52-man detachment was sent to Salonika to act as packhorse handlers for the British contingent.

Following this they returned to Egypt where they took part in the defence of the Suez Canal. In early 1916, the AIF was reorganised and expanded, to prepare it for further operations. In March 1916, the AIF's infantry divisions began transferring to France and Belgium to serve in the trenches of the Western Front. Their first major action in France came at Pozières and Mouquet Farm in July and August 1916, after which over the next two-and-a-half years the 24th Battalion took part in many of the major battles undertaken by the Australians in Europe. In 1917, after the Germans shortened their lines and withdrew to the Hindenburg Line, in May the 24th took part in the Second Battle of Bullecourt where the battalion suffered over 80 per cent casualties, before later in the year attacking around Broodseinde.

In 1918, despite being severely depleted, it played a defensive role during the German spring offensive before supporting the attack at Hamel in July. In August, it joined the Allied Hundred Days Offensive, attacking around Amiens, and then joining the advance that followed. In early October 1918, the battalion attacked the Beaurevoir and then Montbrehain. It was during this final attack, on 5 October, that one of the battalion's subalterns, George Ingram, performed the deeds that resulted in him being awarded the Victoria Cross. At the conclusion of the battle, the 24th was withdrawn from the line for rest and reorganisation and did not take part in further combat before the war came to an end on 11 November 1918. Its strength dwindled as the demobilisation process began and personnel were repatriated back to Australia, and the 24th Battalion was disbanded in May 1919. During its service during World War I the battalion lost 909 men killed and 2,494 men wounded. A total of 19 battle honours were bestowed upon the 24th Battalion in 1927 for its involvement in the war.

In 1921, the decision was made to perpetuate the numerical designations and battle honours of the AIF by re-raising the AIF units as part of the Citizens Forces (later renamed the "Militia"). To a large extent most of these units were raised in the areas from where their personnel had been drawn during the war, thus maintaining their regional links in the process. This was achieved by amalgamating the 2nd and 3rd Battalions of the 24th Infantry Regiment, and subsuming part of the 29th Light Horse Regiment to form a single battalion, The 24th Battalion was raised in Victoria with its headquarters in Surrey Hills, with detachments spread out around the area including depots at Camberwell, Box Hill, Upper Hawthorn, Ringwood and Belgrave. In 1927, territorial designations were adopted by the Citizens Forces and the battalion became known as the 24th Battalion (Kooyong Regiment); the battalion's motto – "I Hold Fast" – was also approved at this time.

Initially, the battalion was manned through a mixture of voluntary and compulsory service; however, in 1929 the Scullin Labor government abolished the compulsory service scheme and replaced it with the all-volunteer Militia. As a result of this, the battalion's strength fell significantly, but it was maintained through recruitment drives. In June 1939, the battalion was merged with the 39th Battalion to become the 24th/39th Battalion and was assigned to the 10th Brigade, 3rd Division.

At the outset of the World War II, due to the provisions of the Defence Act (1903) which prohibited sending the Militia to fight outside of Australian territory, the decision was made to raise an all volunteer force to serve overseas—initial operations were conceived to be likely in the Middle East, France and later possibly the United Kingdom—while it was decided that the Militia would be used to defend the Australian mainland and to improve Australia's overall level of readiness through the reinstitution of compulsory military service and extended periods of continuous periods of training.