Gallagher originated the role of Moritz Stiefel in "Spring Awakening" on Broadway after performing the role Off-Broadway and in workshops at Lincoln Center. The rock musical, with music by Duncan Sheik and a book and lyrics by Steven Sater premiered Off-Broadway at the Atlantic Theatre Company on May 19, 2006 and ran through August 5, 2006. "Spring Awakening" opened on Broadway at the Eugene O'Neill Theatre on December 10, 2006. Gallagher won the 2007 Tony Award for Best Performance by a Featured Actor in a Musical for his performance. On December 16, 2007, he left "Spring Awakening" and was succeeded two days later by Blake Bashoff.