On July 19, 1964 during the Vietnam War at a rally in Saigon, he called for expanding the war into North Vietnam. He then led a military coup on August 16 replacing Duong Van Minh as Prime Minister. At the same time he also established a new constitution, which the US Embassy helped to draft. Khanh held this position for about a year, before being exiled to France by Nguyen Cao Ky.
See also: South Vietnam -- Vietnam War