During a potions lesson Harry throws a Filibuster Firework in Goyle's cauldron of Swelling Solution, which explodes and showers the class with the potion. During the ensuing chaos Hermione slips away and steals the necessary ingredients for the Polyjuice Potion from Snape's private stores. Goyle blunders around the classroom with his hands over his eyes, which have expanded to the size of dinner plates.
Like Crabbe, Goyle is tricked by Harry and Ron into eating cakes laced with a Sleeping Draught. Harry and Ron bundle Crabbe and Goyle into a cupboard, taking some of their hairs and stealing their shoes in preparation for using the Polyjuice Potion.
Goyle attends the Care of Magical Creatures lesson and, alongside Draco Malfoy and Vincent Crabbe, takes over Buckbeak from Harry. After Draco is attacked, the Slytherins all start shouting about Hagrid. Crabbe and Goyle look threateningly at the Gryffindors as they blame Draco for Buckbeak's behaviour.
Goyle helps Malfoy, Crabbe and Marcus Flint in the attempt to sabotage Harry at the match. He supports Malfoy on his shoulders, covered by a long, black cloak, and they pretend to be a Dementor. He is given detention when they are caught, and has fifty points taken from Slytherin.
Goyle attends the Care of Magical Creatures lesson with his fellow Slytherin students. He chuckles as Draco Malfoy questions Hagrid during the lesson, appreciating his friend's sarcasm. Goyle is horrified when Professor Moody Transfigures Malfoy into a ferret later in the afternoon.
Goyle stands with the rest of the Slytherin students in the corridor as they wait for the Potions lesson to begin. When Draco and Harry attack each other, Goyle is hit by Harry's redirected Furnunculus spell, causing great ugly boils to spring up on his face. He is sent to the hospital wing by Professor Snape.
Goyle attends the Care of Magical Creatures lesson with his fellow Slytherin students. When the Blast-Ended Skrewts escape from their boxes and rampage over the pumpkin patch, he flees into Hagrid's cabin with the other students, barricading themselves in for safety.
Goyle stands behind Draco Malfoy in the doorway of Harry, Ron and Hermione's compartment on the Hogwarts Express. He leers at the trio as Draco taunts them about the events at the end of term. Malfoy, Crabbe and Goyle are hit simultaneously by several jinxes performed by Harry, Ron, Hermione, Fred and George, and lie slumped, unconscious on the train floor.
Goyle attends the Apparition lesson in the Great Hall. He and Crabbe have a whispered argument with Draco Malfoy as the students assemble, which ends when Professor McGonagall tells Malfoy to pay attention. During the lesson, he and Crabbe are angrily told by Malfoy to do as they are asked and keep a lookout for him.