Mirren famously won an Oscar for portraying Queen Elizabeth II in director Stephen Frears's critically-acclaimed 2006 film The Queen.
In an interview with Parade, Mirren suggested that the Duchess of Cambridge will be a tremendous asset to the Royal Family.
"We're lucky to have such a true person as Kate Middleton," Mirren explained to the publication.
The actress added: "[Kate is] exactly what the monarchy needs - an ordinary girl. She's going to be terrific."
Mirren will reprise her role of Queen Elizabeth II in a West End stage adaptation of The Audience, which will run from March 5, 2013 to June 15 at the Gielgud Theatre.
Watch a trailer for The Queen.