Great British Bake Off host Giedroyc, who also returns to host the WhatsOnStage Awards this year, will play Frau Schmidt, whilst Olivier award-winning actress Friedman plays Mother Abbess.
They join the previously announced Kara Tointon as Maria and Julian Ovenden – last seen in the Donmar's My Night With Reg – as Captain Georg von Trapp. Coronation Street actress Katherine Kelly (City of Angels) plays Baroness Elsa Schraeder while Alexander Armstrong will play Max Detweiler.
Further casting includes Evelyn Hoskins (Carrie: the Musical) as Liesl von Trapp, Paul Copley (Home), David Bamber (My Night With Reg – Olivier Award winner) and Jon Tarcy.
The production – which will be broadcast live from Three Mills Studios – is directed by Giedroyc's sister, Bafta-nominated Coky Giedroyc.
ITV’s Director of Entertainment and Comedy Elaine Bedell said :
"This is the first time in the UK that this type of project has been attempted – a musical drama both performed and broadcast live – but big ambitious live television events is what ITV does well.
"We've assembled some of the very best talent both in front of and behind the camera and I can't wait to see it all come together."
The two-and-a-half-hour TV show will be based on Rodgers and Hammerstein's 1959 stage musical, which tells the story of trainee nun Maria who becomes a governess to the musical von Trapp family in Austria. It features the classic songs "My Favourite Things", "Edelweiss" and, of course, "The Sound of Music".