The Australian home front during World War II played a significant role in the Allied victory and led to permanent changes to Australian society.

During the war the Government of Australia greatly expanded its powers in order to better direct the war effort, and Australia's industrial and human resources were focused on supporting the Allied armed forces. While there were only a relatively small number of attacks on civilian targets, many Australians feared that the country would be invaded during the early years of the Pacific War. By 1942 the Americans under Douglas MacArthur were arriving in large numbers and used Australia as one base of operations against Japan. In foreign policy reliance on the United States replaced reliance on Britain.

Robert Menzies was sworn in as Prime Minister of Australia for the first time on 26 April 1939 following the death of Joseph Lyons. He led a minority United Australia Party government, after Country Party leader Earle Page refused to serve in a Coalition government led by Menzies. On 3 September 1939, Australia entered World War II, with Menzies making a declaration of a state of war in a national radio broadcast:

My fellow Australians. It is my melancholy duty to inform you, officially, that, in consequence of the persistence by Germany in her invasion of Poland, Great Britain has declared war upon her, and that, as a result, Australia is also at war.

Earle Page as leader of the Country Party and John Curtin as leader of the Labor Party both pledged support to the declaration, and Parliament passed the National Security Act 1939. A War Cabinet was formed after the declaration of war, initially composed of Prime Minister Menzies and five senior ministers (RG Casey, GA Street, Senator McLeay, HS Gullet and World War I Prime Minister Billy Hughes). When Page still refused to join a government under Menzies, he was replaced by Archie Cameron as leader of the Country Party on 13 September 1939, allowing the conservative parties to re-form a Coalition by March 1940.

The recruitment of a volunteer military force for service at home and abroad was announced, the Second Australian Imperial Force, and a citizen militia was organised for local defence. Menzies committed to provide 20,000 men to augment British forces in Europe, and on 15 November 1939 announced the reintroduction of conscription for home-defence service, effective 1 January 1940, freeing volunteers for overseas service.

By June 1940, Germany had overrun the Low Countries, Norway and France leaving the British Empire standing alone against Germany. Menzies called for an ‘all in’ war effort and, with the support of Curtin, amended the National Security Act to extend government powers to tax, acquire property, control businesses and the labour force and allow for conscription of men for the "defence of Australia". Essington Lewis, the head of BHP was appointed Director-General of Munitions Supply to assist with mobilisation of national resources. However, in spring 1940, the coal miners under communist leadership struck for higher wages for 67 days. On 15 June 1940 the Menzies government suppressed 10 communist and fascist parties and organizations as subversive of the war effort. Police and army intelligence made hundreds of raids that night, and later broke up public meetings in the capital cities. In July 1940, the Menzies government imposed regulations under the National Security Act placing virtually all of Australia's newspapers, radio stations, and film industry under the direct control of the Director-General of Information. Newspaper publishers complained it was a blow struck at the freedom of the press. In January 1941, new regulations were directed against speaking disloyalty in public or even in private. The regulations were aimed at "whisperers" who undermined morale by spreading false rumours. During World War II many enemy aliens were interned in Australia under the National Security Act 1939.

Prisoners of war were also sent to Australia from other Allied countries as were their enemy aliens for internment in Australia. About 7,000 residents were interned by Australia, including more than 1,500 British nationals. A further 8,000 people were sent to Australia to be interned after being detained overseas by Australia's allies. At its peak in 1942, more than 12,000 people were interned in Australia.