In November 1960, Thi led the paratroopers in a coup against Diệm, citing political interference in the military. The rebels gained the upper hand but Thi was reluctant to push for a complete victory, and the coup was defeated after Diệm falsely promised to make reforms in order to buy time for loyalists to rescue him. Thi fled into exile in Cambodia, but returned after Diệm was deposed and executed in November 1963. He became the deputy commander of I Corps under Nguyễn Khánh, and helped his superior to overthrow Diệm's subjugators three months later. Thi became the commander of the 1st Division, before taking control of I Corps later in the year.