Thompson would play Oh, the head of MiB. It is unclear whether her character will serve as a replacement for Rip Torn's Zed, who appeared in Men in Black and Men in Black II. Recent legal issues may prevent Torn from returning to the franchise.
Thompson would be joining previously-announced cast members Will Smith, Tommy Lee Jones, Josh Brolin and Jemaine Clement.
Men in Black III is expected to go into production shortly with a script from Etan Cohen and David Koepp. Barry Sonnenfeld will return to the franchise as director. The film is being planned for release on May 25th, 2012.