The project was originally conceived as a film reboot of the film series which started with The Exorcist (1973), until the idea was reworked as a television series sequel instead. This would not materialize up until The Exorcist: Believer (2023).
The creators expressed an intention to work in elements from The Exorcist III (1990) into the third season before the series was canceled. The final scene recreates the famous sequence of the nurse's murder from that film.
Is both a reboot and a sequel to the events of the original movie, as evidenced by the photo of the infamous stairs and a newspaper article recounting some of the events from the first film.
The music played at the end of episode one is Tubular Bells, the same music that is played during the original film of The Exorcist in 1973.
Though a sequel to the book and first movie, the TV series ignores the movie sequels.