Wallace was commissioned in 1969 after graduating from the United States Military Academy at West Point, then qualified as an armor officer before serving in the Vietnam War. After serving in Vietnam, Wallace became a company commander, battalion S-1 (adjutant), and battalion S-3 operations officer with the 82d Airborne Division.
In 1977, he attended the Armor Officer Advanced Course at Fort Knox, Kentucky, and the Naval Postgraduate School in Monterey, California.
In 1983, he joined the 2d Armored Cavalry Regiment in Germany.
As a general officer, he commanded the 4th Infantry Division (Mechanized) and then the Joint Warfighting Center and Director of Joint Training at the U.S. Joint Forces Command in Suffolk, Virginia.
General Wallace assumed command of the V Corps on July 18, 2001. He commanded U.S. ground forces during the 2003 invasion of Iraq until June 14, 2003, when he left to become the commanding general of the Army's Combined Arms Center at Fort Leavenworth, Kansas. His replacement in Iraq was Lt. Gen. Ricardo S. Sanchez.
Wallace assumed command of the United States Army Training and Doctrine Command (TRADOC) at Fort Monroe, Virginia, on October 13, 2005.
| Defense Distinguished Service Medal | |
| Army Distinguished Service Medal with oak leaf cluster | |
| Legion of Merit with four oak leaf clusters | |
| Bronze Star | |
| Meritorious Service Medal with oak leaf cluster | |
| Army Commendation Medal with valor device and two oak leaf clusters | |
| Army Achievement Medal |