On 14 March 1966 he was appointed commander of I Corps, which oversaw the northernmost part of the country, replacing Nguyễn Chánh Thi.[1]: 129 The replacement of the popular Thi by his military rival Nguyễn Cao Kỳ sparked the Buddhist Uprising and Chuẩn supported the Struggle Movement against the junta in Saigon. On 9 April Kỳ replaced Chuẩn with Lieutenant general Tôn Thất Đính in an attempt to shut down the opposition.[1]: 133 [2]
On 9 July 1966 a special military tribunal retired Chuân, Đính, Thi and other officers involved in the uprising.[1]: 143