During World War I, Gillem served with the American Expeditionary Forces in Siberia for eight months from 1918 to 1919.

[2] Then, Gillem taught at the United States Army Infantry School, despite never having graduated there.

Its report, "Utilization of Negro Manpower in the Postwar Army Policy", was presented in April 1946.

When the Third Army headquarters was moved from Atlanta, Georgia, to Fort McPherson in 1947, Gillem also assumed command of the post.

In 1947 Gillem served as an assistant to General George C. Marshall on his presidential mission to China.

Upon the end of his military career, Gillen served for four years as executive director of the National Foundation for the March of Dimes in the 1960s.

On June 21, 1916, Gillem married Virginia Harrison (December 18, 1895 – October 25, 1964) in Nogales, Arizona.

The elder son, Alvan Cullem Gillem II, was born in Nogales in 1917[8] and became a lieutenant general in the United States Air Force.