- For the superhero of the same name, see Kara Danvers.
Kara Zor-El, Superman's (Kal-El) cousin who, after 12 years of keeping her powers a secret on Earth, decides to finally embrace her superhuman abilities and be the hero she was always meant to be. Twelve-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 at 24, Kara lives in National City assisting media mogul and fierce taskmaster Cat Grant, who just hired the Daily Planet’s former photographer, James Olsen, as her new art director. However, Kara's days of keeping her talents a secret are over when Hank Henshaw, head of a super-secret agency where her sister also works, enlists her to help them protect the citizens of National City from sinister threats. Though Kara will need to find a way to manage her newfound empowerment with her very human relationships, her heart soars as she takes to the skies as Supergirl to fight crime.
- "When I was a child, my planet Krypton was dying. I was sent to Earth to protect my cousin. But my pod got knocked off course and by the time I got here, my cousin had already grown up and become... Superman. And so I hid my powers until recently when an accident forced me to reveal myself to the world. To most people, I'm an assistant at CatCo Worldwide Media. But in secret, I work with my adoptive sister for the D.E.O. to protect my city from alien life and anyone else that means to cause it harm. I am Supergirl."
- "When I was a child, my planet Krypton was dying. I was sent to Earth to protect my cousin. But my pod got knocked off course and by the time I got here, my cousin had already grown up and become... Superman. I hid who I really was until one day when an accident forced me to reveal myself to the world. To most people, I'm a reporter at CatCo Worldwide Media. But in secret, I work with my adoptive sister for the D.E.O. to protect my city from alien life and anyone else that means to cause it harm. I am Supergirl."
- Melissa Benoist as Kara Danvers/Supergirl
- Mehcad Brooks as James Olsen/Guardian
- Chyler Leigh as Alex Danvers
- Jeremy Jordan as Winn Schott
- David Harewood as J'onn J'onzz/Martian Manhunter
- Calista Flockhart as Cat Grant (season 1; special appearance season 2—present)
- Floriana Lima as Maggie Sawyer (season 2; recurring season 3)
- Chris Wood as Mon-El (season 2—present)
- Katie McGrath as Lena Luthor (season 3; recurring season 2)
- Odette Annable as Samantha Arias/Reign (season 3) 
Special Guest Stars
- Dean Cain as Jeremiah Danvers
- Helen Slater as Eliza Danvers
- Laura Benanti as Alura Zor-El (seasons 1—2)
- Grant Gustin as Barry Allen/The Flash
- Carlos Valdes as Cisco Ramon/Vibe (season 2)
- Tyler Hoechlin as Clark Kent/Superman (season 2)
- Teri Hatcher as Rhea (season 2)
- Darren Criss as Music Meister (season 2)
- Robert Gant as Zor-El
- Malina Weissman as Young Kara Zor-El (season 1; co-star season 2)
- Chris Vance as Non (season 1)
- Hope Lauren as Jane Doe/Bizarro (season 1)
- Italia Ricci as Siobhan Smythe/Silver Banshee (season 1)
- Laura Vandervoort as Indigo (season 1)
- Glenn Morshower as Sam Lane (season 1)
- Ian Gomez as Snapper Carr (season 2)
- Brenda Strong as Lillian Luthor (season 2—present)
- Sharon Leal as M'gann M'orzz/Miss Martian (season 2)
- Frederick Schmidt as John Corben/Metallo (season 2)
- Andrea Brooks as Eve Teschmacher (season 2)
- Tamzin Merchant as Lyra Strayd (season 2)
- Kevin Sorbo as Lar Gand (season 2)
- Curtis Lum as Demos (season 2)
- DC Comics later incorporated several elements from the show in 2016 when they relaunched the Supergirl comics as part of their DC Rebirth event.
- While all other shows in the Arrowverse primarily take place on Earth-1, this show takes place on Earth-38.
- ↑ CBS Sets Fall Premiere Dates, ‘Supergirl’ Debut Gets ‘Big Bang’ Lead-In - Deadline
- ↑ ‘Supergirl’ Lands CBS’ First New Series Order for 2015-16 Season - Variety
- ↑ ‘Supergirl’ Moves to The CW, Renewed for Season 2 - Deadline
- ↑ http://www.denofgeek.com/us/tv/supergirl/261313/supergirl-season-3-confirmed
- ↑ Supergirl Time Slot, Synopsis and Photos Released - Comicbook.com
- ↑ ‘Supergirl’: Katie McGrath Promoted To Series Regular For Season 3 - Deadline
- ↑ https://supergirl.tv/supergirl-season-3-synopsis
- ↑ http://deadline.com/2017/05/supergirl-odette-annable-cast-reign-season-3-1202105143/