Lin Shaye leads Insidious: The Last Key as Elise Rainier, the parapsychologist whose own childhood home in Five Keys, New Mexico, becomes the case. Shaye had played Elise in all three earlier Insidious films, according to an IANS report on the casting from July 2016, and the official Universal site bills her first for this fourth chapter of the series.
Leigh Whannell plays Specs in Insidious: The Last Key, one half of the investigating duo who work alongside Elise Rainier. Whannell also wrote the screenplay, as he had for every earlier entry, and the official Universal site describes him as one of the creators of the series and the director of Insidious: Chapter 3, so he worked on this film both behind the camera and in front of it.
Angus Sampson returns in Insidious: The Last Key as Tucker, the partner of Specs and the second half of the team that helps Elise Rainier with her cases. Deadline listed Sampson among the returning cast in its August 2016 casting report, alongside Lin Shaye and Leigh Whannell, which made the investigating trio the fixed point of a film whose remaining principal cast was new.
Kirk Acevedo as Ted Garza
Kirk Acevedo plays Ted Garza in Insidious: The Last Key, the man who calls Elise Rainier about a haunting in Five Keys and sets the present day story in motion. Deadline announced Acevedo on August 30, 2016, while the film was shooting, and introduced him through his work as Ramse on the Syfy series 12 Monkeys and in Dawn of the Planet of the Apes.
Caitlin Gerard as Imogen Rainier
Caitlin Gerard plays Imogen Rainier in Insidious: The Last Key, one of the Rainier relatives drawn into the haunting at the family home. Gerard was among the five actors Deadline reported as joining the film in August 2016, and that report pointed to her earlier work in The Social Network and The Awakening. Her character was kept under wraps at the time.
Spencer Locke plays Melissa Rainier in Insidious: The Last Key, another member of the Rainier family whom the haunting reaches in the present day. Deadline's August 2016 casting report introduced Locke through her role as K-Mart in Resident Evil: Extinction and Resident Evil: Afterlife, which gave her a background in genre film before she joined this one.
Josh Stewart as Gerald Rainier
Josh Stewart plays Gerald Rainier in Insidious: The Last Key, part of the Rainier household in the film's 1953 storyline. An IANS report in July 2016, citing Variety, said Stewart had joined the sequel with his role still unannounced and noted his earlier work in The Dark Knight Rises and on Criminal Minds.
Tessa Ferrer as Audrey Rainier
Tessa Ferrer plays Audrey Rainier in Insidious: The Last Key, the mother of the young Elise, and Audrey is killed in 1953 after a demon with keys for fingers gets loose in the house. Ferrer was not named in Deadline's August 2016 casting round, but she appears on the official cast list on Universal's site for the film, where she is billed tenth.
Aleque Reid as Anna
Aleque Reid plays Anna in Insidious: The Last Key, credited ninth in the TMDB billing, just ahead of the younger actors who play Elise and Christian Rainier. Reid is not named in the 2016 trade casting reports or on the cast list of the official Universal site, so her credit here comes from the full TMDB cast list, which runs to 33 names including three uncredited roles.
Ava Kolker plays Elise Rainier as a child in the 1953 prologue of Insidious: The Last Key, one of three actors credited as Elise along with Hana Hayes and Lin Shaye. Deadline reported Kolker's casting in August 2016, citing her recurring role on Girl Meets World and her upcoming work in Lifetime's Sister Cities and the feature Message from the King.
Pierce Pope as Christian Rainier (young)
Pierce Pope plays Christian Rainier as a boy in the 1953 scenes of Insidious: The Last Key, set in Five Keys. The TMDB credits split Christian across three actors, with Thomas Robie as the teenage Christian and Bruce Davison as the adult, so Pope plays the character at the earliest point of a story told across several decades.
Bruce Davison plays Christian Rainier as an adult in Insidious: The Last Key, the oldest of the three actors who share the role in the credits. Deadline announced Davison on August 30, 2016, while the film was shooting, and introduced him through his work as Senator Kelly in X-Men and X2. The official Universal cast list bills him eighth, ahead of Spencer Locke and Tessa Ferrer.