The Arrest and assassination of Ngô Đình Diệm, then president of South Vietnam, marked the culmination of a successful CIA-backed coup d'état led by General Duong Van Minh in November 1963. On the morning of November 2, 1963, Diem and his adviser, younger brother Ngo Dinh Nhu, were arrested after the Army of the Republic of Vietnam (ARVN) had been successful in a bloody overnight siege on Gia Long Palace in Saigon. The coup was the culmination of nine years of autocratic and nepotistic family rule in South Vietnam. Discontent with the Diem regime had been simmering below the surface, and exploded with mass Buddhist protests against long-standing religious discrimination after the government shooting of protesters who defied a ban on the flying of the Buddhist flag.

When rebel forces entered the palace, the Ngo brothers were not present, as they had escaped the night before to a loyalist shelter in Cholon. The brothers had kept in communication with the rebels through a direct link from the shelter to the palace, and misled them into believing that they were still in the palace. The Ngo brothers soon agreed to surrender and were promised safe exile; after being arrested, they were instead executed in the back of an armoured personnel carrier by ARVN officers on the journey back to military headquarters at Tan Son Nhut Air Base.

While no formal inquiry was conducted, the responsibility for the deaths of the Ngo brothers is commonly placed on Minh's bodyguard, Captain Nguyen Van Nhung, and on Major Duong Hieu Nghia, both of whom guarded the brothers during the trip. Minh's army colleagues and US officials in Saigon agreed that Minh ordered the executions. They postulated various motives, including that the brothers embarrassed Minh by fleeing the Presidential Palace, and that the brothers were killed to eliminate a later political comeback. The generals initially attempted to cover up the execution by suggesting that the brothers had committed suicide, but this was contradicted when photos of the Ngos' bloodied bodies surfaced in the media.