He gained notoriety for his flamboyant manner, womanizing, and risky and brash behavior, which deeply concerned South Vietnam's American allies and angered the Vietnamese public, many of whom regarded him as a "cowboy" and "hooligan".
In 1966 Kỳ decided to purge rival General Nguyễn Chánh Thi from a command role, which provoked major unrest in Da Nang and Huế.
Three months of large-scale demonstrations and riots paralyzed parts of the country, and after much maneuvering and some military battles, Kỳ's forces finally put down the uprising, and Thi was exiled, entrenching the former's grip on power.
The election was rigged to ensure that Thiệu and Kỳ's military ticket would win, and strong executive powers meant that the junta, in effect, still ruled.
The commander of a transport squadron, Kỳ was put in charge of Tân Sơn Nhứt Air Base, the main aerial facility in the capital, Saigon.
[13] Some time after the plotters had made their broadcast, Kỳ consolidated the troops on Saigon's outskirts at Tân Sơn Nhứt Air Base, the largest in the country and where the military was headquartered.
Kỳ decided to make a show of force as Phát and Đức began to wilt, and he sent jets to fly low over Saigon and finish off the rebel stand.
The signature of Chief of State Phan Khắc Sửu was required to pass the ruling, but he referred the matter to the High National Council (HNC), a junta-appointed civilian advisory body, to get their opinion.
The deposal prompted US Ambassador Maxwell D. Taylor to angrily berate Thiệu, Thi, Kỳ, and Cang in a private meeting and threaten to cut off aid if they did not reverse their decision.
[26] In January 1965, the junta-appointed prime minister, Trần Văn Hương, introduced a series of measures to expand the anticommunist war effort, notably by widening the terms of conscription.
[31] In early February, Taylor told Kỳ, who then passed on the message to colleagues in the junta, that the United States was "in no way propping up General Khanh or backing him in any fashion.
[36] Shortly before noon on 19 February, Thảo and General Phát used around 50 tanks, and some infantry battalions, to seize control of the military headquarters, the post office, and the radio station of Saigon.
[48] On 20 May, a half dozen officers and around 40 civilians, predominantly Catholic, were arrested on charges of attempting to assassinate Prime Minister Phan Huy Quát and kidnap Kỳ, among others.
[58] Historian Stanley Karnow said of Kỳ and Thi: "Both flamboyant characters who wore gaudy uniforms and sported sinister moustaches, the two young officers had been friends, and their rivalry seemed to typify the personal struggles for power that chronically afflicted South Vietnam.
[58] On one occasion, Kỳ came to I Corps to remonstrate with him in early March, Thi addressed his staff and asked mockingly, "Should we pay attention to this funny little man from Saigon or should we ignore him?
A large segment of the South Vietnamese military was the Regional and Popular Forces, which were militias who served in their native areas, and they appreciated a commander with a regionalistic rapport.
[57] Time magazine reported that Thi "ran it [I Corps] like a warlord of yore, obeying those edicts of the central government that suited him and blithely disregarding the rest.
"[60] Kỳ then gave a series of reasons for dismissing Thi, accusing him of being too left-wing, of ruling the central regions like a warlord, of having a mistress who was suspected of being a communist, and being too conspiratorial.
He then put Quang under house arrest and finally had Thi exiled, cementing his junta's grip on power and ending the Buddhist movement as a political force.
[73] The centre-left Australian Labor Party became more sympathetic to the communists and their leader, Arthur Calwell, stridently denounced Kỳ as a "fascist dictator" and a "butcher" ahead of his 1967 visit.
[79] In an attempt at damage control, the administration of President Johnson denied to the American media that Kỳ had made the remark, claiming it was a fabrication by Moynahan, only to have the air marshal defiantly repeat the statement that Hitler was his only hero.
[83] US policymakers heard rumors that the generals had agreed to subvert the constitution, and The New York Times revealed the formation of a secret military committee that would control the government after the election.
[86] Walt Rostow briefed President Johnson and concluded that the SMC was "in effect, a scheme for 'guided democracy' in which a half dozen generals would decide finally what was good and bad for the country.
On 10 August 57 members of the United States House of Representatives signed a statement condemning Kỳ's electoral malpractices and threatening a review of US policy in Vietnam.
[87] Kỳ and Thiệu were reluctant to campaign and meet the populace as they saw such events as liabilities rather than opportunities to win over the public, and showed little interest in gaining popular support in any case, as they could always count on a rigging of the ballot.
Kỳ and Thiệu decided to campaign indirectly by appearing at set piece ceremonial appointments, such as transferring land titles to peasants, as hostile elements from the general population were less likely to be present.
He often raised eyebrows when he was the military prime minister by arriving at events to meet civilians with his wife in matching black flight suits, boots, blue caps, and silk scarves.
[100] When he was a young pilot, Kỳ once landed a helicopter in the road in front of a girlfriend's house in order to impress her, causing the locals to panic and earning the ire of his commander for misusing military equipment.
In the interview, Kỳ decried the corruption and poverty of South Vietnam, lamented about the inability of the government and the United States to solve their problems, compared the Catholics to the Communists, and openly agreed with many of the social aims of Ho Chi Minh and the Viet Cong.
[109] His daughter from his second marriage, Nguyễn Cao Kỳ Duyên, is well known in the overseas Vietnamese entertainment industry as a mistress of ceremonies and singer on the music variety show Paris By Night.