For much of his time at Hogwarts, Goyle was part of the trio of friends including him, Vincent Crabbe and Draco Malfoy, the latter being the de facto leader of the group. However, Goyle was frequently seen as nothing more than a lackey to Draco; following him around and doing his bidding, when in reality the three truly were close friends. After the Triwizard Tournament and death of Cassius Warrington, Goyle began questioning what he was raised to believe. Goyle was conflicted when Draco went into hiding and refused to join the Death Eaters. Under pressure, Goyle followed through with his initiation and bore the Dark Mark, but instantly regretted the decision. He was often at odds with Crabbe afterwards because of his die-hard belief in the Death Eater ideology, but reluctantly followed through with what he was forced to do after the Death Eaters took over Hogwarts in fear of being killed.
During the Battle of Hogwarts, Goyle defected from the Death Eaters, but was forced to kill Crabbe when he engaged in a duel with him. After the Battle, Goyle reunited with Draco and the two mourned the loss of their friend. Goyle later returned to Hogwarts as part of the "eighth year" students and finished his education. He studied to become a healer, hoping to atone for his sins while part of the Death Eaters. He later married a muggle-born witch a few years his junior and had two children, a boy and a girl; Vincent Draconius and Dianna Adela Goyle.