Born in Ogden, Utah, Ashby grew up in a Mormon household and had a tumultuous childhood as part of a dysfunctional family which included the divorce of his parents, his father's suicide and dropping out of high school. In his late teens, Ashby married but soon after divorced.

As Ashby was entering adult life, he moved from Utah to California where he quickly became an assistant film editor. His big break occurred in 1967 when he won the Academy Award for Film Editing for In the Heat of the Night.

At the urging of its director, Norman Jewison, Ashby directed his first film, The Landlord, in 1970. Over the next 16 years, Ashby directed several acclaimed and popular films, including the off-beat romance Harold and Maude and the social satire Being There with Peter Sellers.

Hal Ashby died of cancer on December 27, 1988 in Malibu, California.