The new season will premiere on the network Jan. 15 and 16 (at 8 PM each night) in a two-part, four-hour event. (All times are ET. Check local listings.)
The recent Our Town revival co-stars Atkinson and Spinella will share the spotlight again as Homeland Security official Karen Hayes and her subordinate Miles, respectively.
"We feel lucky to be working with so many great actors," said executive producer and show runner Howard Gordon in a release. "Each of these newcomers, as well as the previously announced cast additions, will help deliver the thrill ride '24' fans have come to expect."
Atkinson is known for her Tony-nominated turns in Enchanted April and The Rainmaker. Other credits for the British-born actress include Ivanov, All My Sons, The Vagina Monologues, Henry VIII and How I Learned to Drive. She also currently appears in the film "Syriana."
Spinella earned a Tony Award for his Broadway debut in Angels in America: Millennium Approaches and Angels in America: Perestroika. Other credits include A View from the Bridge, Electra, James Joyce's The Dead on Broadway, Svejk Off-Broadway and the recent Los Angeles debut of Stuff Happens. The TV series follows one - rather eventful - day (the title referring to 24 hours) in the life of Counter Terrorist Unit (CTU) agent Jack Bauer (Sutherland), each of the 24 continuous weekly episodes in a season showing what unfolds in one, real-time hour. (A ticking clock occasionally appears, fueling the show's signature intensity.)
Previous "24" co-stars Carlos Bernard, Roger Cross, Gregory Itzin, James Morrison, Louis Lombardi, Mary Lynn Rajskub and Kim Raver will return in the new season. Also joining the cast are Connie Britton (The Exonerated, "Spin City"), Brady Corbet, Jean Smart (The Man Who Came to Dinner, "Designing Women"), Sean Astin ("The Lord of the Rings"), Julian Sands (Stuff Happens, "Boxing Helena"), Peter Weller (The Exonerated, "RoboCop") and JoBeth Williams (Last Dance, "Poltergeist").
"24" was created by Joel Surnow and Robert Cochran. Real Time Productions and Imagine Television produce the show in association with 20th Century Fox Television. Brian Grazer, Surnow, Cochran, Gordon and Evan Katz are the executive producers. Kiefer Sutherland is a co-executive producer.
For more information on "24," visit FOX at http://www.fox.com/24/.