Michael Kovak is the son of a successful funeral home owner and businessman, Istvan. Disillusioned with his job as a mortician, Michael decides to enter a seminary and renounce his vows upon completion, thereby getting a free college degree. Four years later, Michael is being ordained to the rank of deacon at the seminary, after which he writes a letter of resignation to his superior, Father Matthew, citing a lack of faith. Father Matthew, apparently wanting to talk to Michael, attempts to catch up to him on the street. He trips over a curb, causing a cyclist, Sandra, to swerve into the path of an oncoming van, and get critically injured. Seeing Michael's clerical garb, she asks him for absolution before her last breath. The hesitant Michael is unable to refuse; he comforts her and performs a blessing ritual to absolve her of her sins. Seeing how calmly Michael handled the situation, Father Matthew tells Michael that he is called to be a priest despite his unwillingness. He also tells Michael that with the rise in demonic possessions every year, the Church needs more exorcists and says that he has the potential to become one. Father Matthew advises him to go to the Vatican in Rome to attend an exorcism course taught by his friend Father Xavier. Michael agrees after Father Matthew tells him that the Church might convert his scholarship into a student loan that would cost him $100,000 if his resignation is accepted before he takes his vows. If Michael attends the exorcism classes and still wants to leave, then it can be discussed (hinting that he may be free to leave).
In Italy, Michael meets Angelina, also taking the course. He soon learns that she is a reporter who has been asked to cover the course for a newspaper article in the Dominican. Father Xavier notes Michael's skepticism and very tentative faith and asks him to meet a renowned friend, a Welsh Jesuit exorcist named Father Lucas. Michael meets Father Lucas at his home, where he also meets one of the priest's patients: a pregnant sixteen-year-old girl named Rosaria, who is possessed and Lucas is trying to exorcise. It is later revealed that she had been raped and abandoned by her father, which led to her possession. However, Michael remains skeptical, even after witnessing several preternatural events, such as the girl coughing up three long nails and speaking English fluently. She even pointedly reminds Michael of the last patient he anointed and of his loathing for his own father. Angelina requests Michael to relay any information he gets from Father Lucas to her, as the latter has always refused to be interviewed by her, which Michael declines. Rosaria tries to drown herself and is hospitalized. In the hospital, Father Lucas performs another exorcism. Rosaria miscarries; the baby dies from cardiac arrest, and the mother from major hemorrhaging. Disheartened, Father Lucas feels he has failed her. After this Michael decides to confide with Angelina.
After Rosaria's death, Father Lucas begins behaving strangely. Michael and Angelina find him sitting outside his house in the rain. Father Lucas takes them into his house and, knowing himself to be possessed, requests that Michael bring Father Xavier to perform the exorcism. Angelina and Michael try desperately to contact and find Father Xavier, but the latter has gone to Civitavecchia for three days. Michael decides to perform the exorcism himself with Angelina. After constant rebuking by the demon and a long, drawn-out fight, Michael regains his lost faith and is able to force the demon to reveal its name, Baal. He completes the exorcism, saying that he believes the demon exists, and he believes in an all powerful God as well. The demon leaves Father Lucas. Michael bids goodbye to Father Lucas, returning to the United States.
The film ends with Michael, having decided to become a priest after all, receiving a letter that Angelina has published an article on exorcism. Father Michael then enters a confessional to hear a girl's confession in his church.
Anthony Hopkins as Father Lucas Trevant
Colin O'Donoghue as Michael Kovak
Alice Braga as Angelina Vargas
Ciarán Hinds as Father Xavier
Toby Jones as Father Matthew
Rutger Hauer as Istvan Kovak
Marta Gastini as Rosaria
Maria Grazia Cucinotta as Aunt Andria
Arianna Veronesi as Francesca
Andrea Calligari as Vincenzo
Chris Marquette as Eddie
Torrey DeVitto as Nina
Ben Cheetham as Young Michael Kovak
Marija Karan as Sandra
Rosa Pianeta as Woman In Exorcism video
Giampiero Ingrassia as Doctor
Rosario Tedesco as Police Officer
Cecilia Dazzi as Nurse
Attila Bardóczy as Father Xavier's Secretary
Nadia Kibout as Ethnic Nun
Anita Pititto as Vatican Nun
Sándor Baranyai as Concierge
Fabiola Balestriere as Young Girl
Anikó Vincze as Katalin Kovac
Adriano Aragon as Italian Doctor (voice)
Peter Arpesella as Doctor (and additional voices)
Jasper Jacob as Priest
Nico Toffoli as the Demon (uncredited voice)
Beatrice Zentai as Woman In Confessional
loosely based on Matt Baglio's book The Rite: The Making of a Modern Exorcist, which itself is based on actual events as witnessed and recounted by American then-exorcist-in-training Father Gary Thomas and his experiences of being sent to Rome to be trained and work daily with veteran clergy of the practice.