Lieutenant Colonel Toan was relieved of command of the 5th Armored Squadron when his retreating armored elements killed over two dozen South Vietnamese Rangers. He returned to political favor when the officer that relieved him, General Nguyen Chanh Thi, was exiled for his unpopular political views. From 1968 to 1972, Toan served as a brigadier general commanding of the 2nd Infantry Division until being promoted to lieutenant general and becoming assistant operations officer and armor commander in the I Corps Tactical Zone.
During the initial phases of the North Vietnamese Nguyen Hue Offensive in March 1972 (called the Easter Offensive in the West), Toan performed well, especially in the defense of Dong Ha, but he fell under the same cloud as his commander, Lieutenant General Hoang Xuan Lam, when the ARVN defense in I Corps collapsed.
It was at this point that Toan's political connections again became paramount when he was moved south to take command of II Corps after the physical and emotional collapse of General Ngo Dzu. He took command at a point when the Central Highlands had become the second front of the communist offensive. Fortuitously for Toan, his senior U.S. advisor, John Paul Vann was fighting the battle for him. When the conflict settled down to a struggle for the city of Kontum, Toan intelligently attended to administrative matters and left operational control in the hands of Vann and Ly Tong Ba, commander of the 23rd Division.
Toan remained in the command of II Corps until 1974, when he was relieved of command by President Nguyen Van Thieu during an anti-corruption campaign.
During the North Vietnamese Ho Chi Minh Campaign of 1975, Toan was given command of III Corps. It was as commander of the Saigon redoubt during the final battles of the war that Toan faced his greatest challenge. Despite the courage of the 18th Division troops to prevent the Communist forces from entering to the capital, the troops were swamped by vastly superior forces.
Recognizing the situation could not be reversed, Toan escaped from South Vietnam after deceiving Generals Le Minh Dao and Tran Quang Khoi that he would fly to the General Command Headquarters in Saigon to request for more troops. Toan is believed to have carried out the order of President Thieu to assassinate his Deputy Corps Commander General Nguyen Van Hieu on April 8, 1975.