In 1941 Walker received his commission as a second lieutenant of Infantry. He was promoted to first lieutenant in 1942, captain in 1943, major in July 1944, and lieutenant colonel in August 1944. Walker entered active duty for World War II in 1942 as a member of the 22nd Infantry Regiment, a unit of the 4th Infantry Division. He received a commission, completed training with his unit in the United States and England, and commanded a company. He took part in the Utah Beach assault during the Normandy landings as executive officer of the regiment's 3rd Battalion. By the time of Operation Cobra, Walker was in command of a battalion, and he continued to lead his unit until he was wounded during the Battle of Hürtgen Forest. Walker remained hospitalized until June 1945.
In 1965, Walker was promoted to brigadier general and assigned as assistant division commander of the 4th Infantry Division, and deployed with the division to South Vietnam. From April to October 1966 he commanded the 3rd Brigade Task Force, which was subsequently organized as 3rd Brigade, 25th Infantry Division. In October 1966, Walker returned to the 4th Infantry Division as assistant division commander, and he continued to serve in Vietnam until August,1967. After returning to the United States, Walker was assigned to the Continental Army Command as deputy chief of staff for military operations and reserve forces. He was promoted to major general in November 1967. In November 1969 Walker returned to Vietnam, this time as commander of the 4th Infantry Division. He led the division until August 1970.
Senior commands
Walker returned to the Pentagon in 1970 as assistant deputy chief of staff for military operations in the office of the Army's deputy chief of staff for operations. In July 1971 Walker was appointed commander of I Corps in South Korea and promoted to lieutenant general. In Augus, 1972 he returned to the United States as a special assistant for training in the office of the Army Chief of Staff. Walker was assigned as commander of First United States Army at Fort Meade, Maryland in August 1973. He served until August 1974, when he retired from the army.
Mississippi Adjutant General
From 1974 to 1976 Walker lived in retirement on a farm in Union, Mississippi. In February 1976 he returned to military service when he was appointed adjutant general of the Mississippi National Guard. He served in this post until retiring again in 1980.
In 1941 Walker married Margaret Hays Walker. Their children included: Glenn D. Walker, Jr. ; Dr. Michael Walker; and Keith C. Walker. Glenn D. Walker, Jr. served in the army and retired as a lieutenant colonel. Michael Walker became a veterinarian. Keith Walker served in the army, and retired as a lieutenant general. Walker died in Kosciusko, Mississippi on May 3, 2002. He was buried at Memorial Park in Union.