O'Malley has been with the production since the writers began workshopping the property. His character defeats his "base instincts" thanks to the song, "Turn It Off."
"Now it's time to pass the torch, or I guess... sparkly pink vest! My last show will be January 27th," the actor announced via Twitter.
O'Malley earned a 2011 Tony Award nomination for Best Featured Actor in a Musical for his performance. His replacement has not been announced.
"South Park" creators-writers Trey Parker and Matt Stone, and Tony-winning Avenue Q songwriter Robert Lopez collaborated on the script and score to the musical, which earned Tony Awards for Best Book, Best Score and Best Musical.
Co-directed by Parker and Casey Nicholaw, The Book of Mormon opened to critical acclaim March 24, 2011, at the Eugene O'Neill Theatre. Both earned Tony Awards for their work and repeat their duties for the tour.
The Book of Mormon has set design by Scott Pask, costume design by Ann Roth, lighting design by Brian MacDevitt and sound design by Brian Ronan. Orchestrations are by Larry Hochman and Stephen Oremus. Music direction and vocal arrangements are by Stephen Oremus.