James Stewart had difficulty saying his lines on time due to hearing and memory problems. Some of the cast were shocked by his aged appearance. Robert Mitchum recalled, "The picture was all about corpses, but Jimmy looked deader than any of them." Stewart outlived Mitchum by one day in real life.
According to director Michael Winner, Robert Mitchum and Richard Boone were both very drunk when they filmed the final shootout. Winner quipped that it should have been called "Gunfight at Alcoholics Anonymous".
To avoid any copyright violations Michael Winner organized a photo session for the cover of the pornographic book that Marlowe found in the bushes. Among the models taking part was Lindy Benson, who became Robert Mitchum's companion for the duration of filming.
This movie is set in the 1970s but the previous Marlowe movie to this film, Farewell, My Lovely (1975), was actually set in the 1940s, making Robert Mitchum's two Chandler pictures playing Phillip Marlowe discontinuous in their universes in time and thus separate entities.
Part of a 1970s revival cycle of film noir and hard-boiled detective movies which included such non-Chandler fare as Gumshoe (1971), Chinatown (1974), and The Black Bird (1975). Five Chandler filmed adaptations were made around this period including this cinema movie.
Robert Mitchum's interpretation and characterization of Raymond Chandler's Phillip Marlowe detective character was much older and world-weary than the earlier cinematic incarnations of the Marlowe private eye.
Some movie posters for this film featured a long text preamble that read: "Meet Philip Marlowe. The toughest private eye whoever wore a trench coat, slapped a dame, and split his knuckles on a jawbone".
The meaning and relevance of "The Big Sleep" title from Raymond Chandler's source novel and its film versions, "is a euphemism for death; it refers to a rumination in the book about "sleeping the big sleep". As such, in simple terms, the title is a metaphor for death.
The name of Phillip Marlowe (Robert Mitchum)'s detective agency was updated for the 1970s for this movie, it being called "Phillip Marlowe - Commercial and Civil Investigations". In previous Marlowe films, it had been usually known as "Phillip Marlowe - Private Investigations".