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.Ham, p. 57. It was part of a year of travelling for Diệm, who made official visits to the United States and other anti-communist countries.Jacobs, pp. 100–104. 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).

Diệm addressed the Parliament of Australia and was made an honorary Knight Grand Cross of the Order of St Michael and St George, one of the highest imperial honours that can be bestowed on a non-British subject—at the time, Australians were also British subjects. Diệm did not engage in substantive political discussions with the Australian leaders and he spent most of his time at public functions. He was universally extolled by the media, which praised him for what they perceived to be a successful, charismatic, democratic and righteous rule in South Vietnam, overlooking his authoritarianism, election fraud and other corrupt practices. The Australian Catholic leadership and media were particularly glowing towards the South Vietnamese head of state. A member of Vietnam's Catholic minority and the brother of Vietnam's leading archbishop, Diệm had pursued policies in Vietnam favoring his co-religionists. He exempted the Catholic Church from land redistribution, gave them more aid and job promotions, and allowed Catholic paramilitaries to attack Buddhists, who formed the religious majority.

Diệm's visit was a highmark in relations between Australia and South Vietnam. Over time, Diệm became unpopular with his foreign allies, who began to criticise his autocratic style and religious bias. By the time of his assassination in 1963, he had little support. Australia later sent troops to support South Vietnam in the anti-communist fight, but the bipartisanship evaporated during the mid-1960s as the ALP began to sympathise with North Vietnam and opposition to the Vietnam War grew. The ALP later withdrew support for and refused to accept refugees from South Vietnam after winning office, but on the return of the centre right Liberal-National coalition to power in 1975, Vietnamese refugees were allowed to resettle in Australia in large numbers.

Background In 1933, the devoutly Catholic Diệm was appointed Interior Minister of Vietnam, serving under Emperor Bảo Đại. However, a few months thereafter he resigned and became a private citizen because the French colonialists would not give Vietnam any meaningful autonomy.Jacobs, pp. 20–21.Karnow, p. 231. During World War II, the Empire of Japan attacked Indochina and wrested control from France, but when they were defeated by the Allies in 1945, a power vacuum was created.Jacobs, p. 22. The communist-dominated Việt Minh of Hồ Chí Minh fought for Vietnamese independence, while the French attempted to regain control of their colony by creating the French Union-allied State of Vietnam under Bảo Đại. A staunch anti-communist nationalist, Diệm opposed both and attempted to create his own movement, with little success.Jacobs, p. 23. With both the French and the communists hostile to him, Diệm felt unsafe and went into self-imposed exile in 1950.Jacobs, p. 25. He spent the next four years in the United States and Europe enlisting support, particularly among Vatican officials and fellow Catholic politicians in America. The success of the effort was helped by the fact that his elder brother Ngô Đình Thục was the leading Catholic cleric in Vietnam and had studied with high-ranking Vatican officials in Rome a few decades earlier.Jacobs, pp. 26–33.Karnow, p. 233.

In 1954, the French lost the Battle of Dien Bien Phu and the Geneva Conference was held to determine the future of French Indochina.Jacobs, p. 37. The Việt Minh were given control of North Vietnam, while the State of Vietnam controlled the territory south of the 17th parallel. The Geneva agreements, which the State of Vietnam did not sign, called for reunification elections to be held in 1956.Jacobs, pp. 40–42.Karnow, p. 235. Bảo Đại appointed Diệm as his prime minister, hoping that he would be able to attract American aid as the French withdrew from Southeast Asia.Jacobs, pp. 38–39.Karnow, p. 234. Diệm then deposed Bảo Đại in a fraudulent referendum and declared himself president of the newly proclaimed Republic of Vietnam.Jacobs, p. 85.Karnow, p. 239. Diệm received support from the U.S. and other anti-communist countries in the midst of the Cold War. He refused to hold the national elections and asserted that Hồ Chí Minh would rig the ballots in the north, although he had done so himself in deposing Bảo Đại.Jacobs, pp. 98–99.

Meetings and ceremonies Diệm arrived in the capital Canberra on 2 September 1957; his visit was the first by a foreign incumbent head of state to Australia.Edwards (1997), p. 24. He had visited the US in May, and the visit to Australia was the second of three legs in a tour of anti-communist countries in the Asia–Pacific region; Diệm had visited Thailand in August and went on to South Korea after leaving Australia. The magnitude of the ceremonial welcome accorded to Diệm was unseen since the visit in 1954 by Queen Elizabeth II.Torney-Parlicki, p. 210. According to Peter Edwards, a military historian at the Australian War Memorial specialising in the Vietnam War, "Everywhere he was feted as a man of courage, faith and vision", and he noted that Diệm was received with "more ceremony and pageantry" than the visit of Queen Elizabeth II in 1954.

Diệm travelled with five others, including the Minister for Public Works and Communications, the Health Minister, and the Permanent Secretary-General of the Department for National Defense. Ahead of his arrival, the South Vietnamese leader had specifically asked to visit Australian manufacturing sites in Sydney and Melbourne, particularly those in the food processing, textile, shipbuilding and housing industries.

Upon disembarking from his plane at Canberra Airport on the morning of Monday 2 September, Diệm was photographed for The Age and described as a "small but striking figure in a royal blue silk frock coat, long white trousers and black mandarin hat". He was greeted by the Governor-General of Australia Sir William Slim and the Prime Minister of Australia Robert Menzies, and was also introduced to the British High Commissioner Lord Carrington and United States Ambassador William Sebald. He was given a 21-gun salute and a guard of honour by the Royal Australian Air Force, whose fighter jets flew overhead, before making a speech about bilateral relations. Diệm said thanked Australia for its "unflagging support in our most critical hours" and praised relations as being of "a quality normally only found in countries united by long friendship". He said "From our common love for freedom and our determination to keep it, stem the solidarity and friendship between our two countries." The South Vietnamese leader was then hosted for a dinner reception at Yarralumla, the residence of the Governor-General.

The centrepiece of Diệm's visit was a speech to a joint sitting of the Parliament of Australia on Tuesday, September 3, with both the House of Representatives and the Senate in attendance. President Diệm said that "moral and spiritual rearmament" and the "moral unity" of the people were the key factors in fighting the spread of communism. After the speech, Menzies called for three cheers for Diệm at an official parliamentary luncheon. Doc Evatt, the leader of the opposition Australian Labor Party joined in, proclaiming that peace, stability and democracy had been achieved in South Vietnam.Edwards (1992), p. 195. On the same day, Diệm also visited the Australian War Memorial and the Australian National University.

On Wednesday, 4 September, Diệm visited the Royal Military College Duntroon in Canberra, where he watched and addressed a parade of Australian cadets, who were training to become officers. Diệm told the students that they were "comrades of the Free World" and that they would help to defend like-minded countries.Edwards (1992), p. 194. At midday, Diệm left the national capital to begin a two-day stint in Melbourne, the capital and largest city in the southern state of Victoria. He was flown to Melbourne Airport by a Royal Australian Air Force Convair and met by a guard of honour formed by members of the Royal Australian Navy. Diệm was met by Premier of Victoria Sir Henry Bolte and Lieutenant-Governor Sir Edmund Herring, and was the guest of honour at a reception hosted by Premier Bolte at Parliament House. On Thursday, 5 September, Diệm attended official receptions at Melbourne Town Hall and at the residence of the Governor of Victoria, re-emphasising his themes of anti-communism and the bilateral focus on democracy. He also visited three factories and had a private audience with the Catholic Archbishop of Melbourne Daniel Mannix, who was well known for his political power and advocacy in Australia. The next morning, before departing for Sydney, Diệm inspected a textile factory in the inner-northern suburb of Carlton and visited several large-scale public housing estates. At the time, Australia was undergoing a post-World War II population boom and was dealing with housing pressures, an issue that was also confronting South Vietnam following the large influx of northern refugees after the partition in 1954.

The guard of honour and a 21-gun salute that Diệm received at Parliament House was repeated in Sydney and Melbourne, where large crowds cheered Diệm's arrival at the airport and the passing of his motorcade. After arriving in Sydney on Friday, September 6, around midday aboard the RAAF Convair, the South Vietnamese leader was taken outside the capital cities for two days during the weekend, so that he could see the Snowy Mountains Scheme, a large hydroelectricity and irrigation project in highland New South Wales. He returned to Sydney on Sunday, September 8, and left Australia the following evening. In one of Diệm's final functions in Sydney, a minor emergency occurred at the Australia Hotel during a banquet hosted by the Premier of New South Wales, Joseph Cahill. A fire ignited in a pile of rubbish, causing alarm bells to sound for ten minutes, interrupting Premier Cahill when he was making his speech, but no evacuation was required.

At the end of the visit, Menzies bestowed on Diệm an honorary Knight Grand Cross of the Order of St Michael and St George, one of the highest imperial honours that had been bestowed on someone who was not a British subject. In his final comments, Diệm said "I have been enriched by this visit to Australia, for I have noted the vast material and spiritual resources of a people who are hard-working, upright, frank, and loyal in their social, political and international relations." He was met by Governor-General Slim, Prime Minister Menzies, the heads of the branches of the Australian Defence Force, the New South Wales Police Commissioner, and given a guard of honour by 100 soldiers before departing on a Qantas Super Constellation requisitioned for his use. Edwards said of the trip: "Australia had now associated Diệm's survival with its national interest, publicly and without restraint", something that eventually extended to military support against the Vietnamese communists.