Peoples was born in Middletown, Connecticut, the son of Ruth Clara (née Levinger) and Joe Webb Peoples, a geologist. He studied English at the University of California, Berkeley.
Peoples worked as a film editor in the 1970s, and started writing screenplays during this time, but his writing career began when he was hired as co-writer on Blade Runner after director Ridley Scott and screenwriter Hampton Fancher separated over creative differences. Following that film's critical success, Peoples was hired by studios to work on films including Ladyhawke (1985) and Leviathan (1989).
With John Milius, Peoples had written a script in the 1980s to adapt the Sgt. Rock series from DC Comics, in which Arnold Schwarzenegger was originally picked to play the title role of the G.I. hero; the project was revived in 2010 involving Joel Silver and Easy Company, although with expectation to set the narrative in a place other than the battlefields of World War II (and so to make the project independent of the early script).
A number of Peoples' other original screenplays were sold during the 1980s, many undergoing lengthy studio development periods before seeing production, among them: Unforgiven, Soldier, and The Blood of Heroes. The Blood of Heroes was directed by Peoples and starred Rutger Hauer.
Peoples received his greatest recognition for Unforgiven, a script first written in 1976 (as The William Munny Killings) and appearing in theaters in 1992.
Released in the same year as Unforgiven, Peoples' screwball comedy Hero.
Later in 1992, Peoples began work (in collaboration with wife Janet Peoples) on 12 Monkeys (1995), a drama / action film concerned with time travel that was inspired by Chris Marker's experimental short film La Jetée. The film was directed by Terry Gilliam, and was successful both critically and commercially.
In 1998, Soldier was filmed by British director Paul Anderson, albeit on a reduced budget and with additional rewriting by Anderson.
As of February 2015, Peoples has thirteen writing credits (ten for original screenplays, two for stories, and one for source material), as well as five credits for editing, and three credits for directing.
Peoples highest accolades were for Unforgiven, for which ultimately received Oscar, Golden Globe and British Academy nominations, and won L.A. Film Critics (1991) and National Society of Film Critics (1992) awards for best screenplay. Peoples was presented with the Distinguished Screenwriter Award at the 2010 Austin Film Festival.