Maurice has curly light brown hair, a scruffy beard, and blue eyes. When Irene and Burke first arrive, he wears loose, long-sleeved shirts, loose pants, and boots. When out and about, he wears a dark coat, a flannel undershirt, a white shirt beneath that, and a red neckerchief. At the end of the movie, he is pictured wearing a gold chain with a large, curved tooth at the end.
When Carolyn Perron went to see Ed and Lorraine Warren talking about demonic possession, Maurice is shown getting an exorcism through a projector. Ed describes him as a French-Canadian farmer with a third-grade education at best, who was molested by his father. When Valak possessed him, he spoke fluent Latin and an upside-down cross appeared from inside of his belly. He grabbed Lorraine and showed her Valak's true face and terrified her into her bedroom for eight days.
Warning: The following section includes spoilers!
Maurice lived and worked in Biertan, Romania, a mountain town overshadowed by the Abbey of St Carta in 1952. Like most of the villagers in Biertan, he fears the abbey and spits when it is mentioned to ward off evil, despite believing that it's a silly superstition.
He delivered supplies to the abbey for years, and didn't see a single nun until he found Sister Victoria hanging from the window. He moved her to the ice house, where he left her laying down, to preserve the body. After leaving the abbey, he began to have nightmares about what he saw that shook him up greatly.
Upon meeting Father Burke and Sister Irene, he initially believes he must have slept with Irene and Father Burke was either her father or jealous husband. While feeding his goats, he was told to help them on their visit to the abbey. He was initially hesitant and finally relented and agreed to go with them.
On the way to the abbey, Irene tells him that her temporary vows would prepare her for a life of servitude to the lord. He asks her "Would, sister, or will?", implying he already has a bit of Valak attached to him.
Once leaving them at the abbey overnight, he walked back to his horse through the cemetery. He was attacked by a vision outside of the crosses, seeing a nun hanging herself once more. He scrambles back into the crosses and finds she cannot follow him inside, so he takes a cross with him back to town to stay safe. He is seen drinking in The Black Bear bar with the cross beside him the next evening.
He is told that a young girl killed herself, hung herself in her father's barn and that it was the influence of the abbey. He sees the shotgun on the wall and takes it with him to save Father Burke and Irene from Valak's evil. He initially uses his axe to dispatch Sister Victoria's reanimated corpse with Father Burke, who tells him to use the shotgun next time. He tells him he wants to save it for emergencies, implying he doesn't have a lot of ammo.
Upon finding Sister Irene alone in the chapel, he helped Father Burke hold down and then kill the reanimated corpse of Sister Oana, by using the shotgun. He makes the assumption that the evil is free, to which Irene replies that the demon needs a human soul to escape. Upon figuring out that Sister Victoria sacrificed herself so that Valak wouldn't take her soul, he wanted to leave, after admitting he didn't understand what she was saying. After getting Father Burke patched up and confirming they needed the relic to stop Valak, he sat by while Father Burke and Irene cemented her vows. He admits that it is a noble act, much like she said to him on the way to the abbey. In the background, he is seen reloading the shotgun.
In the catacombs, he believes the relic could be anywhere, but Burke reminds Irene of her visions of "Mary points the way." Upon retrieving the relic, he insists that they need to pray first, but Burke replies that there is a time for prayer and a time for action. He follows hesitantly, keeping up with the group until they got to the door that says "God Ends Here". Father Burke breaks off first, and when Irene goes into another room, he starts down the hallway further. Leading with the shotgun, his torch is blown out when he tries to enter another room, and is blasted back by a demonic wind. He drops the torch and runs.
After hearing Irene scream and the door to the main room close, he finds the door and runs at it, throwing himself against it to try and open it. He finally blasts the door open with the shotgun and falls down the stairs into the room full of visions of novitiates with bloody bags on their heads. One of them makes a sound and he aims, but doesn't fire, making his way through the still bodies of them until they part. He finds Irene, floating in the middle of a pentagram with the same sack over her head, already possessed by Valak.
He says that Frenchie let down everyone in his life, and that he should have kept running, and calls him Frenchman. He claims he's French-Canadian and spreads the blood of Christ on Irene's face, sending the demon from her. He pushes her aside just in time to get grabbed and choked, then thrown, leaving Irene falling into the ritual space without him.
When Irene spits the blood of Christ on Valak, supposedly vanquishing him, Frenchie dives into the water to save Irene before she drowns. He takes her to a small alcove and gives her CPR to save her life as the entrance closes. He reminds her that it's called a kiss of life, but it's only called that way because she is a nun now and he knows he shouldn't kiss her. He tells her his real name and she thanks him for saving her life.
After burying the nuns, he questions if the ground was still unholy. Irene asks if he's going back to Bierton and he says he's done with Romania. His father was a tomato farmer and he wants to try that instead. They leave after showing an upside-down cross that looked like a scar on the back of his neck.
Sister Irene starts as a stranger and someone that Frenchie is prone to flirting with, until he finds out that she is a nun. He grows to care for her enough to try and sacrifice himself to save her from Valak's hold at the end of the movie. It is this sacrifice that leads to his own possession.
Father Burke is first seen as a hurdle to leap over, a jealous husband or an angry father, but they seem to grow an accord as he tells Frenchie he needs to take them to the abbey. By the time he shows Burke and Irene the body in the ice house, he seems to cling to the strength offered by Burke, as he's clearly afraid. He tries to warn them not to stay overnight, but they don't listen and he leaves anyway. When he returns, he finds Burke first and is willing to help save him and Irene from harm.
Valak tormented him from the time he found Sister Victoria, oppressing him with nightmares and visions. He kept coming back, strengthening the hold that he had on him, and inevitably ending in his possession. It was through Frenchie that he managed to attach to the Warrens, and also Janet Hodgson.