- Is half Italian and half Jewish.
- Birth name was Max Deitch, but took his mother's maiden name when he became an actor.
- Went to the same high school as Matt Damon, Ben Affleck and Casey Affleck, and studied drama with the same teacher.
- Auditioned for the 1994 biopic Ed Wood, was hired by director Tim Burton and began shooting all in the same day.
- Played actor Paul Marco in Ed Wood; the real Marco tried to evict him from his on-set trailer because the actors had their character names on the doors, leading Marco to believe Casella had taken his dressing room.
- In 1997, played Timon in the original Broadway production of The Lion King.
- Starred with Richard Thomas in a 2011 production of Shakespeare's Timon of Athens at New York's Public Theater.