Carolyn decides to contact Demonologists Ed and Lorraine Warren, who have recently investigated a possessed doll called Annabelle. The Warrens agree to take on the case, conduct an initial investigation and conclude that the house may require an exorcism, but they need authorization from the Catholic Church and further evidence before they can proceed. Ed and Lorraine discover that the house once belonged to an accused witch, Bathsheba (a relative of Mary Towne Eastey), who sacrificed her week-old child to the devil and killed herself in 1863 after cursing all who would take her land. They find reports of numerous murders and suicides in houses that had since been built on the property.

In 1971, Roger and Carolyn Perron move into a dilapidated farmhouse in Harrisville, Rhode Island, with their five daughters Andrea, Nancy, Christine, Cindy, and April. Their dog Sadie refuses to enter the house and one of the children, while playing a game of "hide and clap", finds a boarded-up entrance to a cellar.

On a potential third film, Director James Wan stated, "There could be many more [Conjuring] movies because the Warrens have so many stories." Screenwriters Chad and Carey Hayes have also expressed interest in working on a story for another sequel. However, Wan stated that he may be unable to direct the film due to his commitments to other projects. He stated to Collider.com, "Assuming we are lucky enough to have a third chapter, there are other filmmakers that I would love to sort of continue on the Conjuring world, if we are lucky enough." Wan has also stated that, if a third film was to be made, it would ideally take place in the 1980s. In June 2017, it was announced that a third installment was in development, with The Conjuring 2 co-writer David Leslie Johnson hired to write the screenplay.

Norma Sutcliffe and Gerald Helfrich, the current owners of the house on which the film was based, are suing James Wan, Warner Bros. and other producers, on the ground that their property is being vandalized constantly as a consequence of the film. Entertainment Weekly obtained documents in which the owners affirm various invasions and ratify that they have found numerous objects affiliated with satanic cults. The lawsuit also reveals that the current owners bought the house in 1987 and lived "in peace" until 2012. Both owners are seeking unspecified damages. When questioned, a spokesperson for Warner Bros. declined to comment on the issue.

DeRosa-Grund allied with Producer Peter Safran, and sibling Writers Chad and Carey Hayes were brought on board to refine the script. Using DeRosa-Grund's treatment and the Ed Warren tape, the Hayes brothers changed the story's point of view from the Perron family to the Warrens'. The brothers interviewed Lorraine Warren many times over the phone to clarify details. By mid-2009, the property became the subject of a six-studio bidding war that landed the film at Summit Entertainment. However, DeRosa-Grund and Summit could not conclude the transaction and the film went into turnaround. DeRosa-Grund reconnected with New Line Cinema, who had lost in the original bidding war but who ultimately picked up the film. On November 11, 2009, a deal was made between New Line and DeRosa-Grund's Evergreen Media Group.

The musical score for The Conjuring was composed by Joseph Bishara, who previously collaborated with Director Wan on Insidious (2011). "James asked me early on about [The Conjuring] while the film was still coming together", explained Bishara on his involvement. "The studio and producers were very supportive in allowing him to bring along who he wanted, with many of his longtime crew from Insidious and even earlier returning." Further into the development process, Wan offered Bishara the chance to act in the film, which he had previously done in Insidious. "We talked about music first and then James had mentioned that he might want me to play one of the entities in this. After reading the script it turned out it was Bathsheba," said Bishara. Because of his early involvement, Bishara was given more time to work out the musical palette of the film. "For whatever reason I was hearing brass clustering as an early response to the material, a quiet shimmering flutter tongue effect, and it grew from there", said Bishara on his creative process.

The first promotional images were released in November 2012, introducing Farmiga and Wilson as Ed and Lorraine Warren. A teaser trailer, previously shown at the 2012 New York Comic Con, kicked off the film's marketing campaign in February 2013. Throughout the campaign, the film was promoted heavily as "based on a true story." In the weeks leading up to the film's release, trailers and TV spots began to feature the real-life Perron family. This was followed by a featurette titled The Devil's Hour in which Lorraine Warren and other paranormal investigators explain some of the supernatural occurrences seen in the film.

However, some critics reacted negatively to the film's similarities with films such as The Exorcist and Poltergeist. Indiewire's Eric Kohn explained that, "The Warrens may know how to handle demonic possessions, but The Conjuring suffers from a different invading force: the ghosts of familiarity." Andrew O'Hehir of Salon said the film provided "all the scream-inducing shocks you could want, right on schedule", but thought the central concept – that the innocent women accused and executed in the Salem witch trials "actually were witches, who slaughtered children and pledged their love to Satan and everything!" – was "reprehensible and inexcusable bullshit".

The success of The Conjuring has spawned several related films along with the main series' sequels, including 2014's Annabelle and its 2017 prequel Annabelle: Creation. In addition, two other films featuring supernatural threats first seen in The Conjuring films, The Nun and The Crooked Man, are also in development.

In June 2013, it was reported that New Line Cinema was already developing a sequel. Both Farmiga and Wilson are signed on to reprise their roles for an additional film. The Conjuring 2 was scheduled to be released on October 23, 2015, but in October 2014, Warner Bros. moved the film's release date to an unspecified 2016 release date. On October 21, it was announced that James Wan would return to direct the sequel. On November 11, 2014, the film was set for a June 10, 2016, release. The sequel was later re-written by David Leslie Johnson, with a script from Eric Heisserer. The film will deal with the Enfield Poltergeist case, which occurred in London from 1977 to 1979. Principal photography began in September 2015 in Los Angeles, and concluded in December 2015 in London.