President Ngô Đình Diệm of South Vietnam becomes the first foreign head of state to make a state visit to Australia.

Ngô Đình Diệm was a South Vietnamese politician who was the final prime minister of the State of Vietnam (1954–1955) and later the first president of South Vietnam from 1955 until his capture and assassination during the CIA-backed 1963 coup d'état.

South Vietnam, officially the Republic of Vietnam, was a country in Southeast Asia that existed from 1955 to 1975. It first garnered international recognition in 1949 as the associated State of Vietnam within the French Union, with its capital at Saigon. Since 1950, it was a member of the Western Bloc during the Cold War. Following the 1954 partition of Vietnam, it became known as South Vietnam and was established as a republic in 1955. South Vietnam was bordered by North Vietnam to the north, Laos to the northwest, Cambodia to the southwest, and Thailand across the Gulf of Thailand to the southwest. Its sovereignty was recognized by the United States and 87 other nations, though it failed to gain admission into the United Nations as a result of a Soviet veto in 1957. It was succeeded by the Republic of South Vietnam in 1975. In 1976, the Republic of South Vietnam and North Vietnam merged to form the Socialist Republic of Vietnam.

The Ngô Đình Diệm presidential visit to Australia from 2 to 9 September 1957 was an official visit by the first president of the Republic of Vietnam. It was part of a year of travelling for Diệm, who made official visits to the United States and other anti-communist countries. As with his American trip, Diệm was warmly and lavishly received during the height of the Cold War, garnering bipartisan praise from both the Liberal Party of Australia of Prime Minister Robert Menzies and the opposition Australian Labor Party (ALP).