The nine-member federal jury in Los Angeles returned the unanimous verdict Monday.
A jury has found that Katy Perry's 2013 hit "Dark Horse" copied a 2009 Christian rap song.
The decision came five years after Marcus Gray and two co-authors first sued alleging that "Dark Horse" stole from "Joyful Noise," a song he released under the stage name Flame.
Gray's attorneys argued that the beat and instrumental line featured through nearly half of "Dark Horse" are substantially similar to those of "Joyful Noise."
Perry and the song's co-authors testified during the seven-day trial that none of them had heard the song or heard of Gray before the lawsuit.
"Dark Horse" spent four weeks at No. 1 on the Billboard charts and earned Perry a Grammy nomination.
The case now goes to a penalty phase, where the jury will decide how much the plaintiffs are owed for the copyright infringement.