Robin De Jesús also joins the company of the long-running hit musical.
Williams won the Project Runway Wicked Challenge on November 13.
Full casting for the festival has been revealed.
The Broadway community will gather at Imagine: A Concert of Hope to benefit the Brian Werbel Memorial Fund.
Broadway performers will help raise money to benefit cancer research.
Check out performances from Wicked, Rocky, and If/Then.
Catch stars Andy Karl, LaChanze, Justin Guarini, and more as they brave the sun to sing showtunes.
The production is set to welcome five new cast members later this month.
The one-night-only Indigo Theatre Project event benefited Safe Horizon.