At the age of ten, he was accepted into the American Conservatory Theater (Young Conservatory program) where he studied theater performance throughout his formative years.
As Blaine, Criss features in many musical performances on Glee, which have been released as singles, available for download.
His first performance, "Teenage Dream" by Katy Perry, was featured on the soundtrack album Glee: The Music, Volume 4. According to Billboard, it was the 16th most successful concert tour of 2011, grossing more than million, with total attendance topping 485,000.
From May 21–July 3, 2011, Criss and the cast of Glee performed in Glee Live! All 40 dates sold out, including shows at Staples Center, Nassau Coliseum, and The O Criss is an advocate for LGBT rights, and is an active supporter of The Trevor Project, the leading national organization focused on suicide prevention efforts among lesbian, gay, bisexual, transgender and questioning (LGBTQ) youth.
Blaine attended Dalton Academy and was lead singer of its glee club, The Dalton Academy Warblers.
Blaine initially served as a friend and mentor for Kurt, the bullied gay member of the Warblers' rival glee club, New Directions.