Haldeman was born June 9, 1943 in Oklahoma City, Oklahoma. His family traveled and he lived in Puerto Rico, New Orleans, Washington, D.C., Bethesda, Maryland and Anchorage, Alaska as a child. Haldeman married Mary Gay Potter, known as "Gay", in 1965. He received a bachelor of science degree in astronomy from the University of Maryland in 1967. That same year he was drafted into the Army and served as a combat engineer in Vietnam. He was wounded in combat and his wartime experience was the inspiration for War Year, his first novel.