The popular 2003 American Idol runner-up, 28, will join the cast of the original New York production of the Tony-winning King Arthur send-up Monty Python's Spamalot on Jan. 18, the Associated Press reports.
Aiken will play Sir Robin, a leading role originated when the show first opened in March 2005 by David Hyde Pierce (who is 20 years Aiken's senior).
Robin is described in program notes for the production as "a cowardly knight well versed in the world of musical theater."
"I really couldn't have asked for a more wonderful group of people to work with," Aiken, who will remain with the show through May 4, 2008, said in a statement.
"Let's not lie, the chance to work with legendary creative minds like [director] Mike Nichols and [librettist] Eric Idle is, on its own, a reason to jump at this opportunity," Aiken added.
Said Nichols, "Clay Aiken is amazing beyond that glorious voice. Turns out he is an excellent comic actor and a master of character."