While planning out the dimensions of the set, Ben Wheatley built a scale replica of the film's warehouse in the video game Minecraft.

Wheatley described games such as Counter Strike as a source of inspiration for the film. He also built the set for the film originally on Minecraft.

Armie Hammer said that police appeared on set during the second day of shooting following calls of concern from members of the public in nearby shops having heard gun shots.

Ben Wheatley has stated a big reason he set the film in the 70s is so there would be no mobile phones.

Luke Evans was cast as Vernon but dropped out due to schedule conflicts with Beauty and the Beast (2017). The role was reworked for Sharlto Copley when he was cast.

Ben Wheatley has said that one of the inspirations was an actual F.B.I. report on a Miami shootout.

Olivia Wilde was cast in the lead role, but dropped out.

Sara Dee features in Free Fire and all previous Ben Wheatley movies he's directed for cinema release. She plays the telephone voice.

Ben Wheatley wrote the role of Chris for Cillian Murphy after the actor approached him expressed a desire to be cast in one of his films.

Chris is displeased because the weapons are not as "ordered", but "AR70s". In fact the folding stocks identify them as a version made by Beretta for Special Forces use - the SC70.

Brie Larson and Michael Smiley have both worked with Edgar Wright; he directed Larson in Scott Pilgrim Vs The World and he directed Smiley In Spaced and The World's End.

Sharlto Copley and Sam Riley starred together in Maleficent (2014).

Taylor and Murphy are both in "Peaky Blinders"

Sharlto Copley and Noah Taylor both star in the online streaming series Powers (2015) as Christian Walker and Johnny Royalle.

No CGI was used in the scene where Sharlto Copley's character, Vernon, was being lit on fire. The actor performed the stunt himself with the protection of a fire-retardant suit and four men with fire extinguishers on standby.

The stunt in which the van rolls over Stevo's head was done practically. It was based on a trick from Penn and Teller where one side of the vehicle is heavily weighted down while the other is not. Then the tires are replaced with softer rubber or foam ones. Ben Wheatley demonstrated the stunt himself to prove it was safe.