Performances take place June 13-14 at Nashville's Schermerhorn Symphony Center and feature a full symphony orchestra.
DeGarmo, who rose to fame as the runner-up on "American Idol" in 2004 (check out her audition), has been seen on Broadway in Hairspray and Hair.
"I'm so excited to be working with Studio Tenn in what is shaping up to be a truly magnificent theatre experience," said DeGarmo. "It is a thrill to take on the iconic role of Dorothy in such an imaginative, innovative production in my own hometown."
Studio Tenn managing director Jake Speck said the company decided to revisit the Schermerhorn this season following the overwhelming success of its 2013 production of Les Misérables.
The cast also features Graham Keen as the Scarecrow, Patrick Waller as the Cowardly Lion, Greg Maheu as the Tin Man, Laura Matula as the Wicked Witch of the West, Megan Murphy Chambers as Glinda the Good Witch, Matthew Carlton as The Wizard/Professor Marvel and 40 local munchkins.
Studio Tenn's Wizard will "pay homage to where this classic story has been and what it has looked like in the past," said Studio Tenn artistic director Matt Logan, "but at the same time, we feel the best, most genuine way to honor its spirit of imagination is to unleash our own."
For tickets, visit StudioTenn.com or call (615) 687-6400.