Australia’s Prime Minister at the time of the Japanese attack on Pearl Harbor was John Curtin. Curtin became prime minister on October 7, 1941, about two months before Japan attacked Pearl Harbor on December 7, 1941, in Hawaii.
Because Australia was ahead of Hawaii in time zones, the attack occurred on December 8 by Australian calendar time. Curtin immediately faced a dramatically changed war situation: Japan was advancing across the Pacific, British defenses in Southeast Asia were collapsing, and many Australian troops were still serving in the Middle East against Germany and Italy.
Curtin led Australia through its most dangerous period of World War II. He strengthened cooperation with the United States, worked closely with General Douglas MacArthur, and insisted that Australian forces be redirected toward the defense of Australia and New Guinea. Japan later bombed Darwin and attacked Allied positions across the region.
The question is sometimes confused by the fact that Robert Menzies and Arthur Fadden had been prime ministers earlier in 1941. However, Curtin was the prime minister when Pearl Harbor was attacked and when Australia entered the Pacific War against Japan.