Khiêm would return to Vietnam when the political climate among the generals was more favorable and became Prime Minister under President Nguyễn Văn Thiệu, resigning only in the last month before the fall of Saigon.

[2] On 11 November 1960, Colonels Vương Văn Đông and Nguyễn Chánh Thi launched a coup attempt against President Diêm, but after surrounding the palace, they stopped attacking and decided to negotiate a power-sharing agreement.

[9] One of Khiêm's subordinates, Phạm Ngọc Thảo, a Communist double agent, was planning one of the many coup plots that engulfed Saigon and destabilised the regime, with the help of Trần Kim Tuyến.

[10] Thảo's plans were shelved when an American CIA agent, Lucien Conein, instructed Khiêm, to stop the coup on the grounds that it was premature.

On the morning of the coup, an emotional Khiêm approached General Tôn Thất Đính with tears welling in his red eyes and asked him to keep their conversation confidential.

After the III Corps commander agreed, Khiêm claimed he wanted to cancel the coup, saying "Đính, I think we still have time to talk to the old man.

[14] Khiêm then reported this to Đôn, and claimed that he had placed Chinese medicinal oil into his eyes to irritate and redden them and thus give the appearance he had become remorseful about the coup, in order to test Đính's loyalty to the plot.

[16] The brothers were subsequently executed en route to military headquarters despite being promised safe exile, apparently on the orders of General Dương Văn Minh.

[18] After the 1963 coup, the key figures took the choice jobs in the Military Revolutionary Council, and Khiêm was demoted from being Chief of Staff of the armed forces to the commander of the III Corps that surrounded Saigon.

[19] The coup plot was initiated by Brigadier General Đỗ Mậu, who had been the head of military security under Diem and had a thorough knowledge of the backgrounds of most of the senior officers and their strengths and weaknesses.

[19] Mậu began to seek out other slighted officers, including Khiêm, Generals Khánh and Thi, who had returned from exile after Diêm's death.

[23] According to the plan, Khiêm's III Corps forces would surround the homes of the sleeping junta members in Saigon while Khánh and a paratrooper unit would occupy the military headquarters at Tan Son Nhut Air Base.

[23] On the night of 29 January, Khiêm ordered troops to assume their positions around Saigon, including armored cars and tanks and some elements from the 5th and 7th Divisions.

[1] In August 1964, after Khánh decided to take more power for himself by declaring a state of emergency and introducing a new constitution, Buddhists launched protests against the new junta, claiming that there was a plot to revive the Diêm era by predominantly Catholic groups such as Cần Lao veterans and Đại Việt supporters, pinpointing Khiêm and Thiệu, both Catholics who had been favoured by Diêm.

Khánh claimed the instability was due to troublemaking by members and supporters of the Catholic-aligned Đại Việt (the Nationalist Party of Greater Vietnam), which he accused of putting partisan plotting ahead of the national interest.

[29] After more arguing between the senior officers, they agreed on 27 August that Khánh, Minh, and Khiêm would rule as a triumvirate for two months, until a new civilian government could be formed.

[31] General Huynh Van Cao, a Catholic and former Diệm loyalist, claimed in a 1972 newspaper interview that Khiêm, by then prime minister, had asked him to join the coup.

[39] In the meantime, Khiêm had been putting pressure on Khánh while serving as his ambassador by charging he and the Buddhists with seeking a "neutralist solution" and "negotiating with the communists".

[40] In January 1965, the junta-appointed Prime Minister Trần Văn Hương introduced a series of measures to expand the military and war effort by widening the terms of conscription.

In an attempt to pre-empt his deposal, Hương had backed a plot led by some Đại Việt-oriented Catholic officers, including Thiệu and Nguyễn Hữu Có.

[48] On 19 February, Thảo and General Lâm Văn Phát began their coup attempt, seizing the military headquarters, the post office and radio station.

[53] Thảo had planned for Đôn to become Defense Minister and Chief of Staff of the military, but the Dai Việt insisted on installing the Catholic Khiêm.

The two American generals had lost confidence in Khánh, but the pro-Diêm political ideology being expressed by Thảo's supporters on radio alienated them, as they feared that the coup plotters would destabilize and polarize the country if they took power.

The Marine Brigade commander, General Lê Nguyên Khang, appealed to the US Embassy in Saigon to not allow Khiêm to depart the US.

Whether the rebels were defeated or a deal was struck to end the revolt in exchange for Khánh's removal is disputed, but most believe the latter as the plotters had met Kỳ beforehand and the collapse was rather orderly.

[49][57][58] Although the coup failed and Khiêm did not return, the Armed Forces Council adopted a vote of no confidence in Khánh and Nguyễn Cao Kỳ, and Thi became the most powerful figure in the junta.

Thao was hunted down and killed in mysterious circumstances by other factions with the military leadership,[49][59] while Phát evaded capture for a few years before surrendering and receiving a pardon from Thiệu.