The Before He Cheats hitmaker will lead the cast in the ambitious new project, which is due to air in America on 5 December (13), and the singer admits she was so nervous about stepping into a part made famous by Julie Andrews, she decided to get a little extra practice in.
She tells the Associated Press, "This is a live show on Tv. So this is definitely a challenge for all of us... I wanted to be here (in New York) and have all my lines memorised and everything and be ready for it."
True Blood vampire Stephen Moyer will perform opposite Underwood as Captain von Trapp, while Broadway regulars Audra MCDonald, Laura Benanti and Christian Borle will also appear in the production.
The former American Idol champ has been grateful for her co-stars' help as she prepares for her first big acting job, saying, "It's been really wonderful. Audra and Laura are incredible. Stephen's great. It's nice to be surrounded by that much talent."
Underwood enjoyed a break from The Sound of Music rehearsals on Tuesday (22Oct13) when she was honoured for her philanthropy efforts with the 2013 Artist Achievement Award at the TJ Martell Foundation's 38th Honors Gala in Manhattan.