Mazzie returns to London for the first time since her acclaimed West End debut in Michael Blakemore's production of Kiss Me Kate at the Victoria Palace Theatre in 1999 for which she received an Olivier Award nomination. Her extensive Broadway credits include Kiss Me, Kate, Ragtime, Passion, Man of La Mancha, Into the Woods, Big River, Kismet, Out of This World, The Vagina Monologues and The Trojan Women. Mazzie is also a popular concert artist with her husband, Jason Danieley, who is currently appearing on Broadway in Curtains.

Waddingham's West End credits include Lautrec, Andrew Lloyd Webber's The Likes of Us, Grease and Lloyd Webber and Ben Elton's The Beautiful Game. On British television, she has appeared on Footballers' Wives, Easy Peasy Hollyoaks—Let Loose and The Only Boy For Me.

Directed by Mike Nichols, Spamalot opened on Broadway on March 17, 2005. The London production celebrates its first anniversary on October 17, and the show opened at the Wynn Las Vegas earlier this year. The Broadway cast includes Jonathan Hadary as King Arthur, Lewis Cleale as Sir Dennis, Rick Holmes as Sir Lancelot, Martin Moran as Sir Robin, Jeffrey Kuhn as Sir Bedevere, Tom Deckman as Historian/Prince Herbert and Michael McGrath as Patsy.

Mazzie and Waddingham's casting swap is made possible by an exchange program between American Equity and UK Equity.