After graduating at the top of his class in 1921, Diệm followed in the footsteps of his eldest brother Ngô Ðình Khôi, joining the civil service. Starting from the lowest rank of mandarin, Diệm steadily rose. He first served at the royal library in Huế, and within one year was the district chief, presiding over seventy villages. Diệm was promoted to be a provincial chief at the age of 25, overseeing 300 villages. Diệm's rise was helped by Khôi's marriage to the daughter of Nguyễn Hữu Bài, the Catholic head of the Council of Ministers. Bài was highly regarded among the French and Diệm's religious and family ties impressed him. The French were impressed by his work ethic but were irritated by his frequent calls to grant more autonomy to Vietnamese. Diệm said that he contemplated resigning but encouragement from the populace convinced him to persist. He first encountered communists distributing propaganda while riding horseback through the region near Quảng Trị. Diệm involved himself in anti-communist activities for the first time, printing his own pamphlets. In 1929, he helped to round up communist agitators in his administrative area. He was rewarded with the promotion to the governorship of Phan Thiết Province, and in 1930 and 1931 suppressed the first peasant revolts organised by the communists, in collaboration with French forces. During the violent events, many villagers were raped and murdered. In 1933, with the return of Bảo Đại to ascend the throne, Diệm was appointed by the French to be his interior minister following lobbying by Bài. After calling for the French to introduce a Vietnamese legislature, he resigned after three months in office when this was rejected. He was stripped of his decorations and titles and threatened with arrest.

For the next decade, Diệm lived as a private citizen with his family, although he was kept under surveillance. He was to have no formal job for 21 years. He spent his time on reading, meditating, attending church, gardening, hunting and amateur photography. Being a conservative, Diệm was not a believer in revolutions and confined his nationalist activities to occasional trips to Saigon to meet with Phan Bội Châu. With the start of the Second World War in the Pacific, he attempted to persuade the invading Japanese forces to declare independence for Vietnam in 1942 but was ignored. He founded a secret political party, the Association for the Restoration of Great Vietnam. When its existence was discovered in the summer of 1944, the French declared Diệm to be a subversive and ordered his arrest. He fled to Saigon disguised as a Japanese officer. In 1945, the Japanese offered him the premiership of a puppet regime under Bảo Đại which they organised upon leaving the country. He declined initially, but regretted his decision and attempted to reclaim the offer. Bảo Đại had already given the post to another candidate and Diệm avoided the stigma of being a collaborationist. In September 1945 after the Japanese withdrawal, Hồ Chí Minh proclaimed the Democratic Republic of Vietnam, his Việt Minh began fighting the French. Diệm attempted to travel to Huế to dissuade Bảo Đại from joining Hồ, but was arrested by the Việt Minh along the way and exiled to a highland village near the border. He might have died of malaria, dysentery and influenza had the local tribesmen not nursed him back to health. Six months later, he was taken to meet Hồ in Hanoi, but refused to join the Việt Minh, assailing Hồ for the death of his brother Khoi. Khoi had been buried alive by Việt Minh cadres.

Diệm continued to attempt to gather support for himself on an anti-Vietminh platform. Despite having little success, Ho was sufficiently irritated to order his arrest. Diem narrowly evaded arrest but was given respite in November 1946 when clashes between the French and Vietminh escalated into full scale war, forcing the Vietminh to divert their resources to fighting. Diem then moved south to the Saigon region to live with Thuc. Diem then jointly founded the Vietnam National Alliance, which called for France to grant Vietnam dominion status similar to the Commonwealth of Nations. The alliance was sufficient to generate support to fund newspapers in Hanoi and Saigon respectively. Both were shut down; the editor in Hanoi was arrested and hit men were hired to kill his Saigon counterpart. Diem's activities had gained him substantial publicity and when France decided to make concessions to placate nationalist agitators, they asked him to lobby Bảo Đại to join them. Diem gave up when Bảo Đại made a deal which he felt to be soft, and returned to Huế. In the meantime, the French had started the State of Vietnam and Diem refused Bảo Đại's offer to become the Prime Minister. He then published a new manifesto in newspapers proclaiming a third force different to communism and French colonialism, but raised little interest. In 1950, the Vietminh lost patience, sentenced him to death in absentia, and the French refused to protect him. Ho's cadres tried to kill him while he was traveling to visit his elder brother Ngo Dinh Thuc in the Mekong Delta, where he was the bishop of the Vĩnh Long diocese. Diem then left Vietnam in 1950.

Diem applied for permission to travel to Rome for the Holy Year celebrations at the Vatican. After gaining French permission he left in August with Thuc, apparently destined to become a politically irrelevant figure. Before going to Europe, Diem went to Japan, where he intended to meet Cường Để to enlist support to seize power. Neither this nor an attempt to woo help from General Douglas MacArthur, the American supreme commander in occupied Japan, yielded meetings. A friend managed to organise a meeting with Wesley Fishel, an American academic who had done consultancy work for the US government. Fishel was a proponent of the anti-colonial, anti-communist third force doctrine in Asia and was impressed with Diem. He helped Diem to organise contacts and meetings in the United States to enlist support. It was an opportune time for Diem, with the outbreak of the Korean War and McCarthyism helping to make Vietnamese anti-communists a sought after commodity in America. Diem was given a reception at the State Department with the Acting Secretary of State James Webb. Possibly intimidated, he gave a weak performance in which Thuc did much of the talking. As a result, no further audiences with notable officials were afforded to him. However, he did meet Cardinal Francis Spellman, regarded as the most politically powerful cleric of his time. Spellman had studied with Thuc in Rome in the 1930s and was to become one of Diem's most powerful advocates. Diem managed an audience with Pope Pius XII in Rome before further lobbying across Europe. Diem also attempted to convince Bảo Đại to make him the Prime Minister of the State of Vietnam but was turned down. Diệm returned to the United States to continue lobbying and in 1951 was able to secure an audience with Secretary of State Dean Acheson.

During the next three years he lived at Spellman's Maryknoll seminary in Lakewood Township, New Jersey, and occasionally at another seminary in Ossining, New York. Spellman helped Diệm to garner support among right wing and Catholic circles such as that of Joseph McCarthy. Diem toured the east of America speaking at universities, arguing that Vietnam could only be saved for the "free world" if the US sponsored a government of nationalists who were opposed to both the Vietminh and the French. He was appointed as a consultant to Michigan State University's Government Research Bureau, where Fishel worked. MSU was administering government sponsored assistance programs for cold war allies, and Diệm helped Fishel to lay the foundation for a program later implemented in South Vietnam, the Michigan State University Vietnam Advisory Group. As French power in Vietnam declined, Diệm's support in America made his stock rise.

With the fall of Dien Bien Phu in 1954 to the Vietminh, French control of Vietnam collapsed and Bảo Đại needed foreign help to sustain his State of Vietnam. Realising Diệm's popularity among American policymakers, he chose Diệm's youngest brother Ngo Dinh Luyen, who was studying in Europe at the time, to be part of his delegation at the 1954 Geneva Conference to determine the future of Indochina. Luyen represented Bảo Đại in his dealings with the Americans, who understood this to be an expression of interest in Diệm. With the backing of the Eisenhower administration, Bảo Đại named Diệm as the Prime Minister. The appointment was widely condemned by French officials, who felt that Diệm was incompetent, with the Prime Minister Mendes-France declaring Diệm to be a "fanatic".

The Geneva accords resulted in Vietnam being partitioned temporarily at the 17th parallel, pending elections in 1956 to reunify the country. The Vietminh controlled the north, while the French backed State of Vietnam controlled the south with Diệm as the Prime Minister. French Indochina was to be dissolved at the start of 1955. Diệm's South Vietnamese delegation chose not to sign the accords, refusing to have half the country under communist rule, but the agreement went into effect regardless.

Diệm arrived at Tan Son Nhut airport in Saigon on June 26, where only a few hundred people turned out to greet him, mainly Catholics. Diệm managed only one wave after getting into his vehicle and did not smile. He was not a man of the people and did not intend to become one, being more interested in commanding respect than popular affection.

The accords allowed for freedom of movement between the two zones until October 1954; this was to put a large strain on the south. Diệm had only expected 10,000 refugees, but by August, there were over 200,000 waiting in Hanoi and Haiphong to be evacuated; the migration helped to strengthen Diệm's political base of support. Before the partition, the majority of Vietnam's Catholic population lived in the north. After the borders were sealed, this majority was now under Diệm's rule. The US Navy program Operation Passage to Freedom saw up to one million North Vietnamese move south, most of them Catholic.

The CIA's Edward Lansdale, who had been posted to help Diệm strengthen his rule, led a propaganda campaign to encourage as many refugees to move south as possible. This effort was twofold: to strengthen the Catholic population specifically and the population generally to help win the 1956 reunification elections. This included sending South Vietnamese agents into the north to spread rumours of impending doom, such as Chinese invasion and pillaging, hiring soothsayers to predict disaster under communism, and claiming that the Americans would use nuclear weapons on North Vietnam. Diệm also used slogans such as "Christ has gone south" and "the Virgin Mary had departed from the North", alleging anti-Catholic persecution under Ho Chi Minh. Over 60% of northern Catholics moved to Diệm's South Vietnam, providing him with a source of loyal support.

Diệm's position at the time was weak; Bảo Đại disliked Diệm and appointed him mainly to political imperatives. The French saw him as hostile and hoped that his rule would collapse. At the time, the French Expeditionary Corps was the most powerful military force in the south; Diệm's Vietnamese National Army was essentially organised and trained by the French. Its officers were installed by the French and the chief of staff General Nguyen Van Hinh was a French citizen; Hinh loathed Diệm and frequently disobeyed him.

Diệm also had to contend with two religious sects, the Cao Dai and Hoa Hao, who wielded private armies in the Mekong Delta, with the Cao Dai estimated to have 25,000 men. The Vietminh was also estimated to have control over a third of the country. The situation was worse in the capital, where the Binh Xuyen organised crime syndicate boasted an army of 40,000 and controlled a vice empire of brothels, casinos, extortion rackets, and opium factories unparalleled in Asia. Bảo Đại had given the Binh Xuyen control of the national police for 1.25 m USD, creating a situation that the Americans likened to Chicago under Al Capone in the 1920s. In effect, Diệm's control did not extend beyond his palace.

In August, Hinh launched a series of public attacks on Diệm, proclaiming that South Vietnam needed a "strong and popular" leader; Hinh bragged that he was preparing a coup. This was thwarted when Lansdale arranged overseas holiday invitations for Hinh's officers. Fearing Diệm's collapse, nine members of his government resigned during Hinh's abortive bid for power. Despite its failure, the French continued to encourage Diệm's enemies in an attempt to destabilize him.

Diệm's appointment came after the French had been defeated at the Battle of Dien Bien Phu and were ready to withdraw from Indochina. At the start of 1955, French Indochina was dissolved, leaving Diệm in temporary control of the south. A referendum was scheduled for October 23, 1955 to determine the future direction of the south. It was contested by Bảo Đại, the Emperor, advocating the restoration of the monarchy, while Diệm ran on a republican platform. The elections were held, with Diệm's brother and confidant Ngô Đình Nhu, the leader of the family's Can Lao Party, which supplied Diệm's electoral base, organising and supervising the elections. Campaigning for Bảo Đại was prohibited, and the result was rigged, with Bảo Đại supporters attacked by Nhu's workers. Diệm recorded 98.2% of the vote, including 605,025 votes in Saigon, where only 450,000 voters were registered. Diệm's tally also exceeded the registration numbers in other districts. Three days later, Diệm proclaimed the formation of the Republic of Vietnam, naming himself President.

Under the 1954 Geneva Accords, Vietnam was to undergo elections in 1956 to reunify the country. Diệm, noting that South Vietnam was not a party to the convention, canceled these. Criticising the Communists, he justified the electoral cancellation by claiming that the 1956 elections would be "meaningful only on the condition that they are absolutely free", despite his numerically impossible tally in the 1955 contest.

After coming under pressure from within the country and the United States, Diệm agreed to hold legislative elections in August 1959 for South Vietnam. Newspapers were not allowed to publish names of independent candidates or their policies, and political meetings exceeding five people were prohibited. Candidates were disqualified for petty reasons such as acts of vandalism against campaign posters. In the rural areas, candidates who ran were threatened using charges of conspiracy with the Vietcong, which carried the death penalty. Phan Quang Dan, the government's most prominent critic, was allowed to run. Despite the deployment of 8,000 ARVN plainclothes troops into his district to vote, Dan still won with a 6–1 ratio. The busing of soldiers occurred across the country, and when the new assembly convened, Dan was arrested.

Diệm's rule was authoritarian and nepotistic. His most trusted official was his brother, Ngô Đình Nhu, leader of the primary pro-Diệm Can Lao political party, who was an opium addict and admirer of Adolf Hitler. He modeled the Can Lao secret police's marching style and torture styles on Nazi designs. Ngô Đình Cẩn, his younger brother, was put in charge of the former Imperial City of Huế. Although neither Cẩn or Nhu held any official role in the government, they ruled their regions of South Vietnam, commanding private armies and secret police. Another brother, Ngô Đình Luyện, was appointed Ambassador to the United Kingdom. His elder brother, Ngô Đình Thục, was the archbishop of Huế. Despite this, Thuc lived in the Presidential Palace, along with Nhu, Nhu's wife and Diệm. Diệm was nationalistic, devoutly Catholic, anti-Communist, and preferred the philosophies of personalism and Confucianism.

Diệm's rule was also pervaded by family corruption. Can was widely believed to be involved in illegal smuggling of rice to North Vietnam on the black market and opium throughout Asia via Laos, as well as monopolising the cinnamon trade, amassing a fortune stored in foreign banks. With Nhu, Can competed for U.S. contracts and rice trade. Thuc, the most powerful religious leader in the country, was allowed to solicit "voluntary contributions to the Church" from Saigon businessmen, which was likened to "tax notices". Thuc also used his position to acquire farms, businesses, urban real estate, rental property and rubber plantations for the Catholic Church. He also used Army of the Republic of Vietnam personnel to work on his timber and construction projects. The Nhus amassed a fortune by running numbers and lottery rackets, manipulating currency and extorting money from Saigon businesses. Luyen became a multimillionaire by speculating in piasters and pounds on the currency exchange using inside government information.

Madame Nhu, the wife of his brother Nhu, was South Vietnam's First Lady, and she led the way in Diệm's programs to reform Saigon society in accordance with their Catholic values. Brothels and opium dens were closed, divorce and abortion made illegal, and adultery laws were strengthened. Diệm also won a street war with the private army of the Binh Xuyen organised crime syndicate of the Cholon brothels and gambling houses who had enjoyed special favors under the French and Bảo Đại. He further dismantled the private armies of the Cao Dai and Hoa Hao religious sects, which controlled parts of the Mekong Delta. Diệm was also passionately anti-Communist. Tortures and killings of "communist suspects" were committed on a daily basis. The death toll was put at around 50,000 with 75,000 imprisonments, and Diệm's effort extended beyond communists to anti-communist dissidents and anti-corruption whistleblowers.

As opposition to Diệm's rule in South Vietnam grew, a low-level insurgency began to take shape there in 1957. Finally, in January 1959, under pressure from southern cadres who were being successfully targeted by Diệm's secret police, Hanoi's Central Committee issued a secret resolution authorizing the use of armed struggle in the South. On 20 December 1960, under instruction from Hanoi, southern communists established the National Front for the Liberation of South Vietnam in order to overthrow the government of the south. The NLF was made up of two distinct groups: South Vietnamese intellectuals who opposed the government and were nationalists; and communists who had remained in the south after the partition and regrouping of 1954 as well as those who had since come from the north, together with local peasants. While there were many non-communist members of the NLF, they were subject to the control of the party cadres and increasingly side-lined as the conflict continued; they did, however, enable the NLF to portray itself as a primarily nationalist, rather than communist, movement.

The cornerstone of Diệm's counterinsurgency effort was the Strategic Hamlet Program, which called for the consolidation of 14,000 villages of South Vietnam into 11,000 secure hamlets, each with its own houses, schools, wells, and watchtowers. The hamlets were intended to isolate the NLF from the villages, their source of recruiting soldiers, supplies and information.

The communists in southern Vietnam resolved that "if we are able to kill Ngo Dinh Diem, the leader of the current fascists dictatorial puppet government, the situation would develop along lines more favourable to our side." Accordingly, on February 22, 1957, when Diem made a visit to an economic fair in Ban Me Thuot, a communist cadre named Ha Minh Tri carried out a directive to assassinate the president. He approached Diem and fired a pistol from close range, but missed, hitting the Secretary of Agrarian Reform's left arm. The weapon jammed and security overpowered Tri before he was able to fire another shot. Diem was unmoved by the incident.

There was an additional attempt to assassinate Ngo (as well as his family) in 1962 when two air force officers —acting in unison — bombed the presidential palace.

In 1957, Diệm visited the United States and Australia, where he was hailed as a "leader of the free world". He was widely feted by the media and politicians of both major parties for his anti-communist convictions.

Diệm was the subject of a failed coup, which occurred in 1960.

During the 1946 – 54 war against the French Union forces, the Vietminh, having gained control of parts of southern Vietnam, initiated land reform. During the period of war, rent collection, which hovered at around 50 – 70%, was impossible in some parts of the country, or the Vietminh had compelled landlords to seek safety in the city and confiscated their land, distributing it to the peasants. When Diệm came to power, he reversed these reallocations as upper-class landowners were part of his ideological support base. In the Mekong Delta, 0.025% of landowners owned 40% of the land; most of the land was owned by absentee landlords and worked by tenant farmers. This generated resentment among the populace, as land ownership was highly valued by Vietnamese society. Diệm declared that landlords could collect no more than 25%, but this was not enforced and in some cases the rent levels were higher than those under French colonisation. Under U.S. pressure, in 1956, he limited individual land holdings to 1.15 km², and reimbursed the landlords for the excess, which he sold to peasants. Many landlords evaded the redistribution by transferring the property to the name of family members. In addition, the ceiling limit was more than 30 times that allowed in South Korea and Taiwan, and the 370,000 acres (1,500 km²) of Catholic Church land were exempted. As a result, only 13% of the South Vietnam's land was redistributed, and by the end of his regime, only 10% of the tenants had received any land, at a high cost. This policy failure generated anger, and in turn sympathy to the Vietminh who had given the peasants free land. At the end of Diệm's rule, 10% of the population owned 55% of the land.

Believing that the central highlands may be of strategic importance to the Vietcong or in a potential invasion by North Vietnam, Diệm decided to construct a Maginot Line of settlements. The area, inhabited by Montagnard indigenous people, had been largely allowed local autonomy in previous times, and the locals distrusted ethnic Vietnamese. Diệm initiated a program of internal migration where 210,000 Vietnamese, mainly Catholics, were moved to Montagnard land in fortified settlements. When the Montagnards protested, Diệm's forces confiscated their spears and bows, which they used to hunt for daily sustenance. Since then, and to the present day, Vietnam has been faced with a Montagnard insurgent separatist movement.

In a country where surveys of the religious composition estimated the Buddhist majority to be between 70 and 90 percent, Diệm's policies generated claims of religious bias. As a member of the Catholic Vietnamese minority, he is widely regarded by historians as having pursued pro-Catholic policies that antagonized many Buddhists. Specifically, the government was regarded as being biased towards Catholics in public service and military promotions, as well as the allocation of land, business favors and tax concessions. Diệm also once told a high ranking officer, forgetting that he was a Buddhist, "Put your Catholic officers in sensitive places. They can be trusted." Many officers in the Army of the Republic of Vietnam converted to Catholicism in the belief that their military prospects depended on it. Additionally, the distribution of firearms to village self-defense militias intended to repel Vietcong guerrillas saw weapons only given to Catholics, with Buddhists in the army being denied promotion if they refused to convert to Catholicism. Some Catholic priests ran their own private armies, and in some areas forced conversions, looting, shelling and demolition of pagodas occurred. Some Buddhist villages converted en masse in order to receive aid or avoid being forcibly resettled by Diệm's regime.

The Catholic Church was the largest landowner in the country, and the "private" status that was imposed on Buddhism by the French, which required official permission to conduct public Buddhist activities, was not repealed by Diệm. The land owned by the Catholic Church was exempt from land reform. Catholics were also de facto exempt from the corvée labor that the government obliged all citizens to perform; U.S. aid was disproportionately distributed to Catholic majority villages. Under Diệm, the Catholic Church enjoyed special exemptions in property acquisition, and in 1959, Diệm dedicated his country to the Virgin Mary. The white and gold Vatican flag was regularly flown at all major public events in South Vietnam. U.S. Aid supplies tended to go to Catholics, and the newly constructed Hue and Dalat universities were placed under Catholic authority to foster a Catholic skewed academic environment.

The regime's relations with the U.S. worsened during 1963, as well as heightening discontent among South Vietnam's Buddhist majority. In May, in the central city of Huế, where Diệm's elder brother was the archbishop, Buddhists were prohibited from displaying Buddhist flags during Vesak celebrations commemorating the birth of Gautama Buddha when the government cited a regulation prohibiting the display of non-government flags. A few days earlier, Catholics were allowed to fly religious flags at another celebration where the regulation was not enforced. This led to a protest led by Thich Tri Quang against the government, which was suppressed by Diệm's forces, killing nine unarmed civilians. Diệm and his supporters blamed the Vietcong for the deaths and claimed that the protesters were responsible for the violence. Although the provincial chief expressed sorrow for the killings and offered to compensate the victims' families, they resolutely denied that government forces were responsible for the killings and blamed the Vietcong. The Buddhists pushed for a five point agreement: freedom to fly religious flags, an end to arbitrary arrests, compensation for the Huế victims, punishment for the officials responsible and religious equality. Diệm labeled the Buddhists as "damn fools" for demanding something that, according to him, they already enjoyed.

Diệm banned demonstrations, and ordered his forces to arrest those who engaged in civil disobedience. On June 3, 1963, protesters attempted to march towards Tu Dam Pagoda. Six waves of ARVN tear gas and attack dogs failed to disperse the crowds, and finally brownish red liquid chemicals were doused on praying protesters, resulting in 67 being hospitalised for chemical injuries. A curfew was subsequently enacted. The turning point came in June when a Buddhist monk, Thích Quảng Đức, set himself on fire in the middle of a busy Saigon intersection in protest of Diệm's policies; photos of this event were disseminated around the world, and for many people these pictures came to represent the failure of Diệm's government. A number of other monks publicly self-immolated, and the U.S. grew increasingly frustrated with the unpopular leader's public image in both Vietnam and the United States. Diệm used his conventional anti-communist argument, identifying the dissenters as communists.

As demonstrations against his government continued throughout the summer, the special forces loyal to Diệm's brother Nhu conducted an August raid of the Xa Loi Pagoda in Saigon. The Pagodas were vandalised, monks beaten, the cremated remains of Thích Quảng Đức, which included a heart which did not disintegrate, were confiscated. Simultaneous raids were carried out across the country, with the Tu Dam Pagoda in Huế being looted, the statue of Gautama Buddha demolished and a body of a deceased monk confiscated. When the populace came to the defense of the monks, the resulting clashes saw 30 civilians killed and 200 wounded. In all 1400 monks were arrested, and some thirty were injured across the country. The U.S. indicated their disapproval of Diệm's administration when their ambassador Henry Cabot Lodge visited the Pagoda ex post facto. No further mass Buddhist protests occurred during the remainder of Diệm's rule. During this time, Madame Nhu, who was the de facto first lady because of Diệm's bachelor life, inflamed the situation by mockingly applauding the suicides, referring to them as "barbecues" while Nhu stated "If the Buddhists want to have another barbecue, I will be glad to supply the gasoline."

The pagoda raids stoked widespread public disquiet in the previously apolitical Saigon public. Students at Saigon University boycotted classes and rioted, which led to arrests, imprisonments and the closure of the university; this was repeated at Huế's University. When high school students demonstrated, Diệm arrested them as well; over 1,000 students from Saigon's leading high school, most of them children of Saigon public servants, were sent to re-education camps. Children as young as five were also sent to these camps on charges of anti-government graffiti.

Diệm's foreign minister Vu Van Mau resigned, shaving his head like a Buddhist monk in protest. When he attempted to leave the country on a religious pilgrimage, Diệm had him jailed.

On orders from U.S. President John F. Kennedy, Henry Cabot Lodge, the American ambassador to South Vietnam, refused to meet with Diệm. Upon hearing that a coup d'état was being designed byARVN generals led by General Dương Văn Minh, the United States gave secret assurances to the generals that the U.S. would not interfere. Dương Văn Minh and his co-conspirators overthrew the government on November 1, 1963. The coup was very swift. On November 1, with only the palace guard remaining to defend President Diệm and his younger brother, Ngô Đình Nhu, the generals called the palace offering Diệm exile if he surrendered. However, that evening, Diệm and his entourage escaped via an underground passage to Cholon, where they were captured the following morning, November 2. The brothers were executed in the back of an armoured personnel carrier by Captain Nguyen Van Nhung while en route to the Vietnamese Joint General Staff headquarters. Diệm was buried in an unmarked grave in a cemetery next to the house of the U.S. ambassador.

Upon learning of Diệm's ouster and death, Ho Chi Minh is reported to have said, "I can scarcely believe the Americans would be so stupid." The North Vietnamese Politburo was more explicit, predicting: "The consequences of the 1 November coup d'état will be contrary to the calculations of the U.S. imperialists ... Diệm was one of the strongest individuals resisting the people and Communism. Everything that could be done in an attempt to crush the revolution was carried out by Diệm. Diệm was one of the most competent lackeys of the U.S. imperialists ... Among the anti-Communists in South Vietnam or exiled in other countries, no one has sufficient political assets and abilities to cause others to obey. Therefore, the lackey administration cannot be stabilized. The coup d'état on 1 November 1963 will not be the last."

After Diệm's assassination, South Vietnam was unable to establish a stable government and numerous coups took place during the first several years after his death. While the U.S. continued to influence South Vietnam's government, the assassination bolstered North Vietnamese attempts to characterize the South Vietnamese as supporters of colonialism.