The Girls star posted the snap on Instagram - and revealed that she was willing to cut off her long locks to take on the iconic role.
Writing on the social media site, Allison said: "The transformation begins! My first shoot as Pan. Fun fact: I was all ready to cut my hair, then was told by the folks who actually know what they're doing that a wig works better for everybody. So, December 4th, here we come. #wiglife #peterpanlive #nbc".
Allison Williams takes on the role of JM Barrie's Peter Pan
She also spoke on American TV programme The Today Show, adding: "I sort of very tentatively offered to cut my hair, I was like, 'You know, if it's a thing that would help I could cut my hair,' and they were like, 'You're welcome to do that, we're still gonna put you in a wig.'"
The producers of the show, which follows the success of the live production of The Sound of Music starring Carrie Underwood, said of Allison: "She will reinvent the iconic role of Peter Pan with her wit, her warmth, her dynamic flying and her wonderful musical abilities."
The 26-year-old actress, famous for playing the character of Marnie Michaels on Lena Dunham's hit HBO show, has been taken to the social media site Instagram for several weeks now to tease fans of her new project.
She posted a short video of her first flying lesson a few weeks ago where she also remembered Robin Williams, the acclaimed actor who also once took on the role of Peter Pan in Hook.
"First day of flying lessons for Pan. Thinking about and missing a hero of mine who once did this and left big shoes to fill", Allison wrote.