The battalion was disbanded in 1919 but was re-raised in 1921 as part of the Citizens Force, and adopted the title of "Royal Melbourne Regiment" in 1935.

The 6th Battalion was completely recruited from Victoria, drawing from Melbourne and the surrounding suburbs to the north where four Citizens Force battalions—the 55th, 56th, 63rd and 64th Infantry—were headquartered.

[5] Raising was complete within a fortnight of the outbreak of the war in August 1914 and less than two months later the battalion embarked for overseas on the troop transport Suffolk,[6] forming part of the 2nd Brigade, 1st Division.

Shortly after the landing the 2nd Brigade was transferred from Anzac Cove to Cape Helles to assist in the attack on Krithia.

During the unsuccessful attack, the 6th Battalion suffered heavy casualties, losing 133 men killed or died of wounds.

[13] Later the battalion fought at Ypres, in Belgium, before returning to the Somme in winter, during which time they undertook defensive duties as well as patrols into no man's land.

[15] The battalion continued operations to late September 1918, taking part in the advance towards Herleville, but was then withdrawn from the line for rest and reorganisation and did not see any further combat.

[21] In 1929, following the election of the Scullin Labor government, the compulsory training scheme was abolished and in its place a new system was introduced whereby the Citizens Forces would be maintained on a part-time, voluntary basis only.

This title was officially approved on King George V's jubilee and was a unique honour, as the battalion was at the time the only Australian infantry unit to carry the Royal prefix.

[c][25][26] At the outset of the Second World War, due to the provisions of the Defence Act (1903) which prohibited sending the Militia to fight outside of Australian territory,[27][d] 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 England—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.

[29] During this time the 6th Battalion was called up for a number of periods of continuous service in order to bolster their readiness and undertook garrison duties in Australia.

In 1944, however, the decision was made to disband the unit,[30] as the Australian government sought to reallocate resources to the economy and began the demobilisation process early.

[40] This lasted until August 1982 when due to concerns about the strategic situation following the Russian invasion of Afghanistan, the Australian government announced the expansion of the CMF and decided to raise another battalion in Victoria.