Thơ was appointed to head a civilian cabinet by the military junta of General Dương Văn Minh, which came to power after overthrowing and assassinating Diệm, the nation's first president.

Thơ was not allowed to take part in policy decisions and had little meaningful power, as Diệm's brothers, Nhu and Cẩn, commanded their own private armies and secret police, and ruled arbitrarily.

Minh and Thơ had a plan to try to end the war by winning over non-communist members of the insurgency, believing that they constituted the majority of the opposition and could be coaxed away, weakening the communists.

Following the proclamation of the Republic of Vietnam—commonly known as South Vietnam—by President Ngô Đình Diệm, who had dethroned Bảo Đại in a fraudulent referendum, Thơ was appointed the inaugural ambassador to Japan.

Despite spending most of his time in Tokyo confined to his bed by a fractured hip, Thơ secured reparations from Japan for its imperial occupation of Vietnam during World War II.

While the Army of the Republic of Vietnam (ARVN) General Dương Văn Minh led the military effort against the Hòa Hảo, Thơ helped to weaken the sect by buying off its warlords.

[6] Cụt was eventually surrounded and sought to make a peace deal so he sent a message to Thơ asking for negotiations so that his men could be integrated into mainstream society and the nation's armed forces.

[10] The move was widely seen as an attempt to use Thơ's Mekong Delta roots to increase the government's popular appeal among southern peasants, because Diệm's regime was dominated by family members, Catholics from central Vietnam.

The real power lay with Diệm's younger brothers, Nhu and Cẩn, who commanded private armies and secret police, as well as giving orders directly to ARVN generals.

The US embassy received angry criticism of Thoi's lack of enthusiasm towards implementing the policy, stating, "he is most certainly not interested in land distribution which would divest him of much of his property".

[12] Thơ also retained a degree of influence over domestic economic policies, which ran far behind Diệm's priorities of absolute control over the military and other apparatus through which he maintained his rule.

During a fact-finding mission by General Maxwell Taylor, the chief of the US military, and Walt Rostow, Thơ and Minh complained of Diệm's autocratic ways and religious favoritism towards his fellow Catholics to the disadvantage of the majority Buddhist populace.

[16] In 1962, he told senior US Embassy official Joseph Mendenhall that Diệm's military subordinates invented arbitrary and falsely inflated figures of Viet Cong fighters.

[18][19] In another project, the village of La Vang in Quảng Trị Province near the border with North Vietnam, was the scene of a female apparition in the late 19th century.

Diệm's brother, Ngô Đình Thục, was the Roman Catholic Archbishop of Huế and the foremost religious figure in South Vietnam's nepotistic regime.

[22][23] The committee concluded the Việt Cộng was responsible for the deaths, despite eyewitness accounts and amateur video showing that the government had fired directly at protesters.

[18] During the McNamara Taylor mission to South Vietnam, Thơ confided his belief that the country was heading in the wrong direction to the American delegation, imploring them to pressure Diệm to reform his policies.

[36] Nhu ordered Đính and Colonel Lê Quang Tung, the ARVN Special Forces commander,[37] to plan a fake coup against the Ngô family.

According to Thơ's assistant, Nguyễn Ngọc Huy, the presence of Generals Trần Văn Đôn and Tôn Thất Đính in both the civilian cabinet and the MRC paralysed the governance process.

[44] Saigon newspapers, which had re-opened following the end of Diệm's censorship, reported that the junta was paralysed because all twelve generals in the MRC had equal power.

Thơ claimed that he had countenanced Nhu's brutal Xá Lợi Pagoda raid, attempting to prove that he would have resigned were it not for Minh's pleas to stay.

Thơ publicly stated that he expected a "rational attitude" coupled with "impartial and realistic judgments" and said that it was part of the provisional government's quest to "clear the way for a permanent regime, which our people are longing for".

[49] With the fall of Diệm, various American sanctions that were implemented against South Vietnam in response to the repression of the Buddhist crisis and Nhu's Special Forces' Xá Lợi Pagoda raids, were lifted.

Thơ contradicted Nhu's earlier reports on the success of the program, claiming that only 20% of the 8,600 existing strategic hamlets were under Saigon's control, with the rest having been taken over by the communists.

The government was criticised for firing large numbers of district and provincial chiefs directly appointed by Diệm, causing a breakdown in law and order during the abrupt transition of power.

One high profile and heavily criticised non-removal was that of General Đỗ Cao Trí, the commander of the ARVN I Corps who gained prominence for his particularly stringent anti-Buddhist crackdown in the central region around Huế.

[52] Thơ recalled in later years that his government's plan was to generate support among the Cao Đài, Hòa Hảo and ethnic Cambodian minorities, elements of which were in the NLF and bring them back into the mainstream fold out of the insurgency into a non-communist pro-West political system.

[58] The number of rural attacks instigated by the Viet Cong surged in the wake of Diệm's deposal, due to the displacement of troops into urban areas for the coup.

The increasingly free discussion generated from the surfacing of new and accurate data following the coup revealed that the military situation was far worse than what was reported by Diệm.

The incidence of Việt Cộng attacks continued to increase as it had done during the summer of 1963, the weapons loss ratio worsened and the rate of Viet Cong defections fell.