Born in Phan Rang in the south central coast of Vietnam, Thieu joined the communist-dominated Việt Minh of Hồ Chí Minh in 1945 but quit after a year and joined the Vietnamese National Army (VNA) of the French-backed State of Vietnam. He gradually rose up the ranks and, in 1954, led a battalion in expelling the communists from his native village. Following the withdrawal of France, the VNA became the ARVN and Thiệu was the head of the Vietnamese National Military Academy for four years before becoming a division commander and colonel. In November 1960, he helped put down a coup attempt against President Ngô Đình Diệm. During this time, he also converted to Roman Catholicism and joined the regime's secret Cần Lao Party; Diệm was thought to give preferential treatment to his co-religionists and Thiệu was accused of being one of many who converted for political advancement.