Jeanne Moreau and the other key actors filmed their scenes in both French and English. Two separate edits were made for the respective markets. The blu-ray/DVD released by the British Film Institute contains the English edit.
The film was shot on location in and around the tiny village of Le Rat, in the Corrèze département of central France. The entire production team stayed in what accommodation they could find locally for the duration of the shoot.
Tony Richardson originally wanted Marlon Brando for the male lead, but scheduling could not be arranged.
Voices for French actors being dubbed into English include (inevitably) Robert Rietty and David De Keyser, two of the busiest dubbing artists in Europe. More unusually, Frank Finlay dubs Gabriel Gobin in the role of the police sergeant, whilst Mark Dignam provides the English voice for the priest, played by Georges Douking.
The screenplay was apparently written with Romy Schneider in mind for the leading role - she was very keen on the idea, and Sam Spiegel had some notion of producing it, although he was not sure about it. Joseph Losey was keen to direct it. Spiegel refused to pay Jean Genet the $50,000 he was asking for the script, but Tony Richardson did pay it, and both Schneider and Losey found themselves no longer involved.