He was appointed prime minister on 29 August 1941, during World War II, following the resignation of Robert Menzies of the United Australia Party (UAP).

Intended as a stop-gap, he was elected Deputy Leader and appointed acting-leader because Archie Cameron and John McEwen had tied in a vote for the leadership.

The Labor Party declined to enter a war cabinet led by Menzies, though Curtin offered co-operation – though not to the extent of supporting conscription for overseas service.

New Country Party leader Arthur Fadden became Treasurer and Menzies unhappily conceded to allow Earle Page back into his ministry.

Curtin took a seat on the newly created Advisory War Council in October 1940 and agreed to a plan by Menzies to travel to Washington and London.

In January 1941, Menzies flew to Britain to discuss the weakness of Singapore's defences and sit with Winston Churchill's British War Cabinet.

In Menzies' absence, Curtin co-operated with Deputy Prime Minister Arthur Fadden in preparing Australia for the expected Pacific War.

After four months, Menzies returned to Australia to face a lack of enthusiasm for his global travels and a war-time minority government full of intrigue and under ever increasing strain.

With the threat of Japan imminent and with the Australian army suffering badly in the Greek and Crete campaigns, Menzies re-approached the Labor Party to form a War Cabinet.

Australia marked 2 years of war on 7 September 1941 with a day of prayer, on which Prime Minister Fadden broadcast to the nation an exhortation to be united in the ‘supreme task of defeating the forces of evil in the world".

With the Pacific on the brink of war, Opposition leader John Curtin offered friendship and co-operation to Fadden, but refused to join in an all-party wartime national government.

[2] Curtin proved a popular leader, rallying the nation in the face of the danger of invasion by the Japanese after Japan's entry into the war in December 1941.