Retired parapsychologist, Elise Rainier, reluctantly uses her spiritual ability to contact the spirit of Quinn Brenner's mother, Lillith, who died a year before. However, she urges Quinn not to make contact with her mother again after a demonic figure continues to haunt her, becoming increasingly malevolent as time progresses and leaving Quinn with her neck injured after the demon flings her around her bedroom. Sean tries to convince Elise, who like him is still grieving after the loss of her husband Jack, to help his daughter, but Elise declines, stating that her previous visits to the "dark" spiritual world made her realize that an evil spirit is hunting to kill her. However, she is convinced by her fellow parapsychologist, Carl, to continue using her spiritual ability, reminding her about her successful case involving Josh Lambert and stating that she is stronger than any spirits or demons because she is living and they are not.
Due to Elise's refusal, Alex suggests to call the demonologists Specs and Tucker, but Quinn's possession grows increasingly worse as she, now possessed by the demon, breaks through her braces. Realizing that they are scammers, Sean prepares to kick the duo out until Elise arrives timely. Deducing that the demon's goal is to lure potential victims to "the Further" so it can eat their life force, Elise decides to enter the spiritual world with Specs and Tucker recording any activities and words she spells out. With the help of a spirit who likewise is a victim of the demon, Elise enters the Further and after a brief encounter with the evil spirit that haunts her, the Bride in Black/Parker Crane, meets with Jack, whom she realizes is the demon. While managing to defeat the demon, Elise returns to the material world after realizing that Quinn has to defeat the faceless version of herself by herself, who is slowly taking control of her features and soul. Though Quinn is at first at a disadvantage, Elise reads a message that the Brenners' late neighbor had tried to tell Quinn of: that Lillith is leaving her with a letter to read before she graduated. Lillith's spirit then appears to help Quinn fully take control of her body and return to the material world. She then disappears after leaving parting words to her family.
Following the Brenner' successful case, Elise decides to come out of retirement and work with Specs and Tucker. She arrives home and notices a figure watching her from outside. Thinking that it is Jack at first, Elise realizes that it is something demonic as the demon suddenly appears beside her.
On September 15, 2013, a third installment in the Insidious series was announced, with Leigh Whannell signed on to return as writer, and Jason Blum and Oren Peli set to produce. When asked about returning for another sequel, actor Patrick Wilson went on to say that he "[doesn't] know where else it could go", and that "[Josh Lambert has] been through the wringer, and I think the movie sets it up well at the end [...] And that's great, that's how it should end." On November 13, 2013, it was announced Focus Features and Stage 6 Films would release the film on April 3, 2015. The date was later moved to May 29, 2015.
On March 11, 2014, Screen Rant reported that the third film would not focus on the Lamberts, but on a new family and story, and would not connect to the last scene in the second film. It was also reported that both Whannell and Angus Sampson would return as ghost hunters Specs and Tucker, along with Lin Shaye as Elise. On May 7, 2014, Wan tweeted that Whannell would direct the third film, which marks his directorial debut. In June 2014, Stefanie Scott and Dermot Mulroney were cast in the film. On September 22, 2014, during the Cinema Diverse Film Festival in Palm Springs, actress Ele Keats said she had recently wrapped an undisclosed supporting role in the film.
Principal photography began on July 9, 2014, in Los Angeles under the title "Into The Further", on a scheduled 29 day shoot. Several scenes were shot in the San Fernando Valley at the Delfino Studios in Sylmar, where the Brenner apartment's interiors were built.
A first look image was released on July 22, 2014. Filming wrapped on August 18, 2014.
The musical score for Insidious: Chapter 3 is composed by Joseph Bishara, who composed the music for the previous installments. A soundtrack album for the film was released digitally on June 5, 2015 by Void Recordings.
A first teaser poster was released online on September 18, 2014, featuring a grey wall with a vent and the red text "The man who can't breathe, the man who lives in the vents, I heard him saying your name last night, I heard him in your room while you were gone, he's in there right now, standing in your room." The first teaser trailer for the film was released by Focus Features on October 23, 2014. The same day director Leigh Whannell invited fans to join him for a live Q&A session on the movie's official Facebook page. A few days later, on October 28, 2014 the same Facebook page reached 4 million fans. On December 17, 2014, fans were invited to connect with Insidious on Kik Messenger for exclusive content.
On March 16, 2015, Focus Features debuted a teaser for the full official trailer that was eventually released the following day, on March 17, 2015, during a series of launch events in selected cities, including Miami (where lead star Stefanie Scott held a Q&A session), Chicago (with supporting actress Hayley Kiyoko in attendance), and New York City (where Fangoria Magazine hosted a Q&A session with Lin Shaye). A new poster featuring Stefanie Scott was also released the same day. On July 3, 2014, Focus Features moved the already announced US theatrical release date from April 3 to May 29, 2015. On December 10, 2014, the distribution company announced that the theatrical release date had been moved back again from May 29 to June 5, 2015.
On May 20, 2015, Focus Features relaunched their Gramercy Pictures label for action, horror, and science fiction movies. Insidious: Chapter 3 was the first release from the revived Gramercy.
Insidious: Chapter 3 grossed $52.2 million in North America and $60.6 million in other territories, for a worldwide total of $112.8 million, against a budget of $10 million.
In North America, the film made $1.6 million from its early Thursday night showings, from 2,150 theaters, and $10.4 million on its opening day, from 3,003 theaters. It finished at third place in its opening weekend, earning $23 million behind fellow opener Spy and holdover San Andreas.
Outside North America, Insidious: Chapter 3 grossed $14.3 million in its opening weekend, from 42 countries on 2,989 screens, also finishing in third place behind San Andreas and Spy. It had the biggest opening for a horror film in the Philippines ($1.5 million) and in Vietnam ($620,000), the second-biggest in Malaysia ($1.6 million), and had similarly successful openings in Russia and the CIS ($2.7 million). Mexico opened with $1.8 million and India with $620,000.
The review aggregator website Rotten Tomatoes lists a 58% approval rating based on 113 reviews and a rating average of 5.5/10. The site's critical consensus reads, "Insidious: Chapter 3 isn't as terrifying as the original, although it boasts surprising thematic depth and is enlivened by another fine performance from Lin Shaye." On Metacritic, which assigns a normalized rating, the film has a score of 52 out of 100 based on 26 critics, indicating "mixed or average reviews". In CinemaScore polls, cinema audiences gave the film an average score of "B+" on an A+ to F scale.
Daniel Krupa of IGN awarded it a score of 7.1 out of 10, saying "Insidious: Chapter 3 is the most focussed, dark, and creepy installment of the series to date." Scott Foundas of Variety gave the film a negative review, saying "Chief among things that go bump in the night in Insidious: Chapter 3 is the movie itself - a thuddingly dull prequel to James Wan's very enjoyable (and highly profitable) demonic-possession horror franchise." Justin Lowe of The Hollywood Reporter gave the film a positive review, saying "Insidious: Chapter 3 offers a relatable young protagonist and several key supporting players from the prior films in a nimble setup to the series." Kyle Anderson of Entertainment Weekly gave the film a C+, saying "Insidious Chapter 3 is the worst kind of sequel: Not terrible, but also cartoonishly unnecessary." Michael Ordoña of the San Francisco Chronicle rated it zero out of four stars, saying "Insidious: Chapter 3 is simply not scary. Not a bit, not a whit. Except that the audience will be terrified of the next stabbing of their eardrums, at generally predictable intervals." Michael O'Sullivan of The Washington Post gave the film one and a half stars out of four, saying "The Insidious franchise, after three attempts to exorcise its real demons, still can't seem to shake what really haunts it: the ghost of B-movies past." Peter Howell of the Toronto Star gave the film two and a half stars out of four, saying "This prequel to the shriek hell, directed and scripted by series writer/actor Leigh Whannell, manages to avoid the Curse of the Triple Cash Grab."
Kerry Lengel of The Arizona Republic gave the film three out of five stars, saying "Insidious: Chapter 3 is almost more a spoof of a classic like The Exorcist than it is an homage. It's not scary horror, it's silly horror, and the audience is in on the joke." Stephen Whitty of the Newark Star-Ledger gave the film two and a half stars, saying "You need more than a few sudden noises and scary shocks to make a good horror movie. But Insidious: Chapter Three is at least an OK horror movie." James Berardinelli of ReelViews gave the film two and a half out of four stars, saying "They say the third time's the charm. Not with the Insidious series, it isn't. Admittedly, installment #3 is an improvement over #2, but it fails to reach the highs of the chilling-but-uneven original." Tim Robey of The Telegraph gave the film four out of five stars, saying "It manages the all-important jump scares with the finesse of a skilled stage illusionist, but it’s the surprisingly sincere emotional core that makes it the pick of the series." Katie Rife of The A.V. Club gave the film a B-, saying "The motif of grief runs throughout Insidious: Chapter 3, which is surprisingly thematically rich for the third installment of a horror franchise. This emotional undercurrent informs the fright scenes, which otherwise lean rather heavily on jump scares." Bilge Ebiri of New York Magazine gave the film a negative review, saying "This is so often the problem with this genre — scary setups, followed by dopey resolutions — that you sort of want to give the movie a pass. But given its distinguished forebears, Insidious: Chapter 3 doesn’t quite live up to expectations."
In an interview Leigh Whannell was asked "If there is a fourth Insidious film, would that be a sequel to Chapter 3, another prequel to the original or will it continue in this timeline or go to a whole new timeline?" Whannell stated: "I don't know. I haven't really thought about it yet. But for the purposes of this interview, I'll say that I'd like to explore the time between this film and the first film. That whole area there where Elise has rediscovered her gift, I think you could have a lot of adventures before she arrives. So I think there is a lot of room there. We've kind of established Lin [Shaye] in this particular film as kind of this superhero, so that would be kind of interesting to explore in the other films."
Insidious: The Last Key was announced in May 2016 for a release date of October 20, 2017. Whannell will return to write, Blum, Peli and Wan producing as well as Shaye reprising her role as Elise Rainer and Adam Robitel directing. The film will now open January 5, 2018.