Xuân started his career in the Vietnamese National Army of the French-backed State of Vietnam and worked in military security and was made an ARVN general, but was later put into a minor job by Diệm.

Xuân then led a group that arrested Diệm and his younger brother and chief adviser, Ngô Đình Nhu, after their hiding place was discovered.

During 1964, Xuân was a member of the ruling junta, and served as the mayor of Saigon and the head of the National Police, during which time he was accused of arresting people for ransom.

Khánh was able to find evidence and his military tribunal convicted them of "lax morality", and being unqualified to command due to a "lack of a clear political concept".

[1] When Diệm became Prime Minister of the State of Vietnam, Xuân fought for him as an officer in the Vietnamese National Army (VNA) in the Battle for Saigon in May 1955, against the Bình Xuyên organised crime syndicate that sought to take over the capital.

Quan was Minh's deputy, and Lắm had been the commander of Diệm's Civil Guard until defecting mid-way through the coup once a rebel victory seemed assured.

Two further officers made up the convoy: Major Dương Hiếu Nghĩa and Captain Nguyễn Văn Nhung, Minh's bodyguard.

As the convoy on the route to the Joint General Staff headquarters, Xuân ordered the APC to stop over at a National Police station where he brutally tortured Nhu and Diệm, asking them where they had hidden money.

[12][13] At the time, French President Charles de Gaulle was contemplating recognising the People's Republic of China and wanted Southeast Asia neutralised as part of his agenda to cultivate relations with the communist bloc.

[14] Khánh told various American officials that Generals Xuân, Đôn, Minh, and Lê Văn Kim were "pro-French and pro-neutralist" and part of de Gaulle's plan.

[16] Khánh had Xuân arrested, along with Minh, Đôn, Kim and Tôn Thất Đính, claiming that they were part of a neutralist plot with the French.

[17] The tribunal then "congratulated" Xuân and his colleagues, but found that they were of "lax morality", unqualified to command due to a "lack of a clear political concept".

[17] Worried that Xuân and his idle colleagues would plot against him, Khánh made arrangements to send them to the United States for military study, but this fell through.