Season 3 (Supergirl)

Supergirl was renewed for a third season by The CW on January 8, 2017. It premiered on October 9, 2017.

Main cast

 * Melissa Benoist as Kara Danvers/Supergirl and Kara/Overgirl
 * Mehcad Brooks as James Olsen and James Olsen's Earth-X doppelgänger
 * Chyler Leigh as Alex Danvers
 * Jeremy Jordan as Winn Schott
 * Katie McGrath as Lena Luthor
 * Odette Annable as Samantha Arias/Reign
 * Chris Wood as Mon-El
 * David Harewood as J'onn J'onzz/Martian Manhunter

Special appearance by

 * Calista Flockhart as Cat Grant
 * Jessica Parker Kennedy

Special guest cast

 * Floriana Lima as Maggie Sawyer
 * Helen Slater as Eliza Danvers
 * Grant Gustin as Barry Allen/The Flash
 * Carlos Valdes as Cisco Ramon
 * Stephen Amell as Oliver Queen/Green Arrow and Oliver
 * Victor Garber as Martin Stein/Firestorm
 * Jesse L. Martin as Joe West
 * Emily Bett Rickards as Felicity Smoak/Overwatch
 * Caity Lotz as Sarah Lance/White Canary
 * Tom Cavanagh as Harrison "Harry" Wells and Eobard Thawne/Reverse-Flash
 * Dominic Purcell as Mick Rory/Heat Wave
 * Candice Patton as Iris West
 * Franz Drameh as Jefferson Jackson/Firestorm
 * Danielle Panabaker as Caitlin Snow/Killer Frost
 * Keiynan Lonsdale as Wally West/Kid Flash

Recurring cast

 * Sharon Leal as M'gann M'orzz/Miss Martian
 * Brenda Strong as Lillian Luthor
 * Andrea Brooks as Eve Teschmacher
 * Curtis Lum as Demos
 * Erica Durance as Alura Zor-El
 * Adrian Pasdar as Morgan Edge
 * Carl Lumbly as M'yrnn J'onzz
 * Emma Tremblay as Ruby Arias
 * Amy Jackson as Imra Ardeen/Saturn Girl
 * Jesse Rath as Brainiac 5

Synopsis
''Thirteen-year-old Kara escaped the doomed planet Krypton with her parents' help at the same time as the infant Kal-El. Protected and raised on Earth by her foster family, the Danvers, Kara grew up in the shadow of her foster sister, Alex, and learned to conceal the phenomenal powers she shares with her famous cousin in order to keep her identity a secret. Years later, Kara was living in National City and still concealing her powers, when a plane crash threatened Alex's life and Kara took to the sky to save her. Now, Kara balances her work as a reporter for CatCo Worldwide Media with her work for the Department of Extra-Normal Operations (D.E.O.), a super-secret government organization whose mission is to keep National City and the Earth safe from sinister threats. At the D.E.O., Kara works for J'onn J'onzz, the Martian Manhunter, and alongside her foster sister, Alex, and best friend, Winn Schott. Also in Kara's life are media mogul Cat Grant, James Olsen, a photo journalist who moonlights as Guardian, a masked vigilante, Lena Luthor, and Mon-El of Daxam, whose planet was ravaged by Krypton's destruction. As Kara struggles to navigate her relationships and her burgeoning life as a reporter, her heart soars as she takes to the skies as Supergirl to fight crime.''

Confirmed plot points

 * The "New 52" Supergirl villain known as Reign has been confirmed to be the season's "Big Bad".
 * Project Cadmus will continue its war against the D.E.O. and Supergirl.
 * The plot of the third season will revolve around what "means to be human", being something that will be addressed with all the characters.
 * James Olsen/Guardian will have a new love interest, and will return to his roots as a journalist and photographer.
 * Cat Grant will appear in multiple episodes in the season.
 * Lyra Strayd will return in this season and she will appear in more episodes than the last season.
 * Kara Danvers will have new upgrades in her suit.
 * Laurie Metcalf has been cast as Winn Schott's mother. She is scheduled to appear in episode 15.

Confirmed new characters

 * Querl Dox/Brainiac 5: Half computer, half organic life and boasting a 12-level intellect, Brainiac 5 is a member of the Legion of Super-Heroes who travels to National City from the 31st Century to help Supergirl and the DEO battle Reign.
 * Tormock: A warrior of Amazonian stature, jacked, tough and brutal, she is a fierce alien prisoner. Dangerous and angry, she gets into a violent fight.