Vy returned to South Vietnam after the 1963 coup which removed Diem from power and led to his assassination. He was arrested during the January 1964 South Vietnamese coup for being a member of the military committee command staff, under General Dương Văn Minh (or "Big Minh"). It was the late President Diem and his brother Ngo Dinh Nhu who want to open talks with the North Vietnamese. Like most of the military leaders involved in the alleged plot, he was soon released. He rose to the rank of Lieutenant General, and was appointed Chief of Staff of the Army of the Republic of Vietnam in 1967.