Haldeman was born 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. He had to repeatedly start classes as a new kid in local schools.
In 1965, Haldeman married
Mary Gay Potter, known as "Gay". He received a BS degree in Physics and Astronomy from the University of Maryland in 1967.
He was immediately drafted into the United States Army, where he served as a combat engineer in Vietnam. He was wounded in combat and received a Purple Heart. His wartime experience inspired his first novel War Year. In addition, in his later books such as The Hemingway Hoax and
Old Twentieth, he continued to explore through fiction the experience of combat soldiers in Vietnam and other wars, both during the wars and after return home.
In 1975, he received an MFA degree in Creative Writing from the University of Iowa Writers' Workshop.
Haldeman resides alternately in Gainesville, Florida and Cambridge, Massachusetts. Since 1983, he has been an Adjunct Professor teaching writing at the Massachusetts Institute of Technology. MIT serves as the setting for his 2007 novel, The Accidental Time Machine. Haldeman is also a painter.
In 2009 and 2010, Haldeman was hospitalized for pancreatitis.