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. In 1975, he received a MFA in Creative Writing from the University of Iowa Writers' Workshop. He currently resides in Gainesville, Florida and Cambridge, Massachusetts and teaches writing at MIT. In addition to being an award-winning writer, Haldeman is a painter. In 2009, and 2010, he has been hospitalized for pancreatitis.
Haldeman's most famous novel is The Forever War (1975), inspired by his Vietnam experiences, which won both the Hugo and Nebula Awards. He later turned it into a series. Haldeman also wrote two of the earliest original novels based on the 1960s Star Trek TV series universe, Planet of Judgment (August 1977) and World Without End (February 1979). In October 2008 it was announced that Ridley Scott will direct a feature film based on The Forever War for Fox.
Haldeman has written at least one produced Hollywood movie script. The film, a low-budget science fiction film called Robot Jox, was released in 1990. He was not entirely happy with the product, saying "to me it’s as if I’d had a child who started out well and then sustained brain damage".
He is a lifetime member of the Science Fiction and Fantasy Writers of America (SFWA), and past-president.
Haldeman is the brother of Jack C. Haldeman II (1941-2002), also a science-fiction author whose work included an original Star Trek novel (Perry's Planet, February 1980).