He was also a Death Eater and was caught with a group of them and his own father who headed the Department of Magical Law Enforcement at the time, sent him to Azkaban.
However, Crouch rescued his son as a favor to his dying wife, and kept him under an invisibility cloak at all times. Berta Jorkins discovered the truth, and years later it reached Lord Voldemort. He rescued Barty Crouch Jr. and put his father under the Imperius Curse. Barty Crouch kidnapped Mad-Eye Moody and, with the help of the polyjuice potion, took over Moody's job of teaching Defense Against the Dark Arts.
The Triwizard Tournament was being held that year and Crouch had to make sure that Harry won. When Harry touched the Triwizard Cup it took him to a graveyard, and his blood was planned to be used to bring Voldemort back to power. The plan succeeded, except for the fact that Harry escaped.
Crouch than planned to kill Harry, but didn't succeed. Under the influence of a powerful truth potion, he told what had happened. His soul was sucked out of him when he was kissed by a dementor.