In 1963, Có came to prominence for his role in the November coup that deposed Vietnam's president, Ngô Đình Diệm, who was assassinated. Có's superior, General Tôn Thất Đính, moved him into command of the 7th Division to lock loyalist forces out of Saigon. Có was promoted to brigadier general after the coup, and as South Vietnam was inflicted with a cycle of coups over the next two years, he became more prominent as other generals defeated one another in power struggles.