The brigade was formed in late 1945 following the end of World War II as part of the Australian contribution to the British Commonwealth Occupation Force (BCOF) in Japan.

As a result, shortly after Japan's capitulation, the Australian prime minister, Ben Chifley made a formal offer of troops for occupation duty.

[8] This resulted in a large epidemic of sexually transmitted diseases throughout occupying allied forces, with the 34th Brigade having a rate of 55% infection amongst its ranks.

[7] In October the New Zealanders also withdrew,[10] and shortly thereafter, as a result of the stable security situation in Japan, the Australian government decided to reduce its contribution to the Allied occupation force from a full brigade, to just one infantry battalion, as well as one fighter squadron and supporting personnel[7] in an effort to build up the newly established Australian Regular Army.

[3] In early 1950, the Menzies government announced that it would finally withdraw all its forces later in the year, although the outbreak of the Korean War prevented this and ultimately 3 RAR remained in Japan until September 1950 when it was deployed to Korea,[5] where it served as part of the 27th Commonwealth Brigade.