Janney will play top CIA agent Elaine Crocker in the Paul Feig-helmed comedy.
"Spy" will also feature Academy Award nominee Melissa McCarthy ("Bridesmaids," "Mike & Molly"), Jason Statham ("Redemption," "The Expendables"), Rose Byrne ("Annie," "Bridesmaids"), Tony nominee Jude Law (Hamlet, Indiscretions), Tony nominee and Emmy winner Bobby Cannavale (Mauritius, The Motherf**ker With the Hat), Curtis "50 Cent" Jackson, Miranda Hart ("Call the Midwife," "Miranda") and Morena Baccarin ("Homeland," "The Good Wife").
Janney is a two-time Tony nominee who has performed in Present Laughter, A View from the Bridge and 9 to 5. Her screen credits include "The West Wing," "American Beauty" and "Mom."
Along with directing, Feig wrote the script for "Spy," and is producing through his Feigco along with Chernin Entertainment and Peter Chernin, Jenno Topping and Jessie Henderson.
Fox is set to release the film Memorial Day 2015.