Dr. Nguyễn Tôn Hoàn (1917 – 19 September 2001) was Vietnamese Catholic politician, originally a physician, who led the Đại Việt Quốc Dân Đảng (Nationalist Party of Greater Vietnam) from the 1940s to the 1960s. He was active in South Vietnamese politics during that time, serving briefly as Deputy Prime Minister in 1964.
Nguyễn Tôn Hoàn was born in Tây Ninh, Vietnam in May 1917. He studied medicine at the University of Hanoi, where he became involved in student politics. In 1939, he helped found the Đại Việt Quốc Dân Đảng (Nationalist Party of Greater Vietnam).
When the Việt Minh gained a foothold over northern Vietnam in 1946, he fled to China, then under the rule of Chiang Kai-shek's nationalist Kuomintang, hiding under the deck of a junk. Hoàn returned to Saigon — where the Việt Minh did not exercise the tight control they possessed in the north—in 1947 to continue his political activism.
In mid-1947, he joined forces with Ngô Đình Diệm, later to become the first President of South Vietnam. A fellow Catholic, Diệm was a former provincial governor in the 1930s and the younger brother of Ngô Đình Khôi, another provincial leader slain by the communists. For the rest of the year, the pair tried to organise anti-communists into a new nationalist body known as the Vietnam National Alliance (VNA). Both wanted to build a Third Force for Vietnam, that avoided communism on one hand and colonialism on the other. Hoàn's Đại Việt and Diệm's power base generated some momentum.
According to Hoàn and Diệm, the objective of the purpose of the VNA was to mobilise support for a new political movement under Bảo Đại, who had been forced to abdicate by the Việt Minh during the August Revolution and went into overseas exile. Bảo Đại then tried to recruit politicians such as Hoàn to provide him with a conduit to power. The French also wanted to work with Bảo Đại so that he would lend more legitimacy to their colonial presence in Vietnam.