He is portrayed by Paul Bettany, who also portrays Bill Cox.
Silas is an albino numerary of the Catholic organization Opus Dei, who practices severe corporal mortification (he is seen using a metal cilice and flogging himself). During the events of the main storyline, he is about forty years old. The film portrays him as younger. The novel depicts him as a monk, although Opus Dei has no monks. Silas's real name is unknown. He had originally lived in Marseille with his parents. However, his father was furious at having an albino for his son, and blamed Silas's mother, repeatedly beating and eventually killing her. Enraged, Silas murdered his father using a butcher's knife and fled. He was only seven years old.
Silas grew up on the streets, eating garbage and waste. Other young runaways excluded him due to his strange appearance. After he pummelled a girl for making fun of his condition, police gave him an ultimatum to either leave Marseille or go to prison. He moved to Toulon, where he continued living on the streets. After getting into a fight with two sailors, he killed one, and was imprisoned in Andorra in the Pyrenees until freed by an earthquake that destroyed the prison walls. He found refuge with a young Spanish priest named Manuel Aringarosa, who gave him the name Silas, after a person in the Bible who was the companion of Paul of Tarsus, imprisoned at Philippi and freed by an earthquake after singing (Acts 16:25-26). Aringarosa eventually became a bishop and the head of Opus Dei.
Before the story's main narrative, Aringarosa puts him in contact with an enigmatic figure called The Teacher and tells him that the mission he will be given is of utmost importance in saving the true Word of God. Under the orders of The Teacher, he murders Jacques Saunière and the other three leaders of the Priory of Sion in order to extract the location of the Priory's clef de voûte or "keystone". However, Silas is reluctant to commit murder, knowing that it is a sin and does so only because he is assured his actions will save the Catholic Church. Shortly after Silas kills Saunière, Harvard professor Robert Langdon is suspected by the French police to be the murderer and goes on the run with the help of Saunière's granddaughter Sophie Neveu.
Silas follows the information given by the Priory leaders to the Church of Saint-Sulpice. However, he discovers that he was duped with false information, and he also kills Sister Sandrine Bieil who had spied on him in the church. The Teacher later tells Silas to go to Château Villette, the residence of Sir Leigh Teabing where Langdon and Sophie have sought refuge, saying that the keystone was there. Silas enters the house and injures Langdon but is subdued by Teabing and Sophie. After being bound and gagged with duct tape, Silas is taken by the three and Teabing's butler Rémy Legaludec to London via Teabing's private jet.
At London, after Teabing, Langdon, and Sophie enter the Temple Church to search for clues to the Grail, Rémy releases Silas and reveals to him that he works for the Teacher. He instructs Silas to get the keystone, kidnap Teabing, and leave by the limousine. Little does Silas know that Teabing is actually the Teacher. Teabing calls Silas from the rear compartment of the limousine and tells him to go to the London Opus Dei Centre for some rest, but at the same time makes an anonymous call to the police and informs them of Silas's whereabouts.
After resting in his room in the Centre for some time, Silas suddenly feels a little uneasy. He looks out the window and sees police cars. Panicking, he attempts to escape, fighting policemen along the way. Almost naked, he runs out from the Centre successfully but is shot by a policeman below the ribs and accidentally shoots Bishop Aringarosa, who had just arrived.
After carrying Aringarosa to the St Mary's Hospital, he vows to kill the Teacher, but Aringarosa pleads with him, saying that if he has learned anything from his teachings, he must know that "Forgiveness is God's greatest gift."
In his last moments, Silas goes out to Kensington Gardens alone and prays to God for mercy and forgiveness. Closing his eyes, he says a final prayer before dying.
In the film, the adult Silas was portrayed by Paul Bettany, and the young Silas by Hugh Mitchell. Silas' story in the film is similar to that in the novel, except for a few minor aspects. Instead of murdering his father for killing his mother, Silas stabs his father on the shoulder for attacking her. After this, his wounded and terrified father screams to him that "you are a ghost" ("Eres un fantasma...!!!"), referring to his albinism. His age during these events is set in Silas's late teens, instead of the age of seven as it happened in the book. He is also portrayed to have killed two assailants who were attacking Aringarosa. Also, in the novel Silas knows that Remy is the Teacher's minion, but in the film he is tricked into believing that Remy is the Teacher. His death is also slightly different. After realizing he had just shot Aringarosa, Silas collapses in anguish and remorse. He then raises his gun and is shot down by the police, his last words being "Soy un fantasma..." ("I am a ghost..."). Also, in the novel, Silas' nationality is French: he tells Aringarosa that he does not speak Spanish. In the film, Silas is Spanish (presumably Basque) and speaks several lines of Spanish.