The 29-year-old actor - who plays Finn Hudson in the US comedy-drama, which also features Dianna Agron, Naya Rivera and Matthew Morrison - will exit the show after the end of the next series, along with Lea Michele, who plays Rachel Berry, and Chris Colfer (Kurt Hummel), according to the programme's creator Ryan Murphy.
He told the Hollywood Reporter: "We made that decision and I involved Chris and Lea and they thought that was a good idea. They both trust the writing and trust me and felt that it would be great to have an open and closed experience for them to go out while they were on top."
But Ryan admitted he is yet to discuss the departure of Finn with Cory, adding: "He knows he was a sophomore when the show started."
The trio's characters are set to graduate from McKinley High at the end of the third series, and Ryan revealed there will be further departures.