The Rite is a fictionalized account of The Rite: The Making of a Modern Exorcist (2009), a book by freelance journalist Matt Baglio. Baglio based his book on his acquaintance with Father Gary Thomas, a parish priest from Saratoga, California, who was tasked by the local bishop to become an exorcist for the diocese. Baglio and Thomas met in 2005 while Baglio was participating in a seminar on exorcism in Rome in preparation for writing his book. The screenplay was written by Australian film writer Michael Petroni.

Those who have both read the book and seen the movie say that the film bears little resemblance to the book. For example, Father Gary Thomas, the subject of the book, was 52 years old, ordained in 1983, had been a priest for 22 years, serving the last 15 years at a parish in Saratoga before he was called to study exorcism in Rome. In the movie, his counterpart, Michael Kovak (Colin O'Donoghue), is a 22-year-old, nonordained student who entered the seminary to get a free four-year education and to get away from having to follow in the footsteps of his mortician father. Matt Baglio, the journalist who followed Father Thomas and wrote his story, is replaced by a young female journalist, Angelina Vargas (Alice Braga), in order to give the demon some sexual fodder. To further show how little resemblance the movie has to the book, the following disclaimer is shown at the end of the film as the credits begin to roll: While inspired by actual events, this movie is a work of fiction and contains fictional and dramatized scenes, characters and dialogue. Any similarity between a fictional character and any actual person is entirely coincidental and unintentional.

Dry materials such as straw or cotton are sometimes placed in a corpse's mouth to prevent embalming fluid or other body fluids from seeping out the mouth, a phenomenon known as 'purging'.

Her cause of death is not mentioned. Because Michael's father says, 'The pain is gone...God has taken it away,' some viewers have suggested she might have died of cancer or some painful disease.

Father Gary Thomas.