Mauer began as a Swing with the Broadway company of Phantom in 1995 and later played the role of romantic lead Raoul in two separate stints 1996-98 and 1999-2001, including the tenth anniversary performance in 1998. He holds the record for performances as Raoul on Broadway, at over 1,500 times. Mauer went on to play the title role on the national tour from January 2004 to April 2006. When the Broadway production become the longest-running show in Broadway history on January 9, 2006, Mauer was one the dozen U.S. Phantoms to take part in the festivities celebrating that milestone.
In addition to Phantom, Mauer has appeared on Broadway as Enjolras in Les Misérables. His national touring credits include The Music of Andrew Lloyd Webber and the Harold Prince production of Show Boat, in which he appeared opposite his wife, Bethe Southard. She played Christine opposite his Phantom at certain performances on the Phantom national tour. Regional credits include Jesus in Jesus Christ Superstar, Anthony in Sweeney Todd and Frederick in The Pirates of Penzance.