Kara Zor-El (Melissa Benoist) was sent to Earth from the doomed planet Krypton as a 13-year-old by her parents Zor-El (Robert Gant) and Alura (Laura Benanti). Alura gave her instructions to protect her infant cousin Kal-El, and informed her that she, like her cousin, would have extraordinary powers under Earth's yellow sun. Kara's spacecraft was knocked off course by a shock wave from Krypton's explosion and forced into the Phantom Zone, where it stayed for 24 years. During this period, time became suspended for Kara and when the spacecraft eventually escaped the Phantom Zone, she was still a 13-year-old girl. By the time the spacecraft crash landed on Earth, Kal-El had grown up and become Superman (Tyler Hoechlin). After helping her out of the craft, Superman took Kara to be adopted by his friends, the Danvers family. The series begins eleven years later when the now 24-year-old Kara is learning to embrace her powers after previously hiding them.
In the first season, Kara Danvers becomes Supergirl. Having hid her powers for more than a decade, believing that Earth did not need another hero, Kara is forced to reveal her powers to thwart an unexpected disaster, setting her on her own journey of heroism as National City's protector. Kara discovers that hundreds of the criminals her mother prosecuted as a judge on Krypton are hiding on Earth, including her mother's twin sister Astra (also played by Benanti) and Astra's husband Non (Chris Vance), who seek to rule the world. After briefly becoming suspicious of the true agenda of her boss, Hank Henshaw (David Harewood), she and her adoptive sister, Alex Danvers (Chyler Leigh), secretly discover that Henshaw is actually benevolent Green Martian refugee J'onn J'onzz, who assumes Henshaw's identity some fifty years after escaping a holocaust on Mars. He infiltrated the DEO to reform the organization and keep watch over Kara. Over the course of the season, Kara is targeted by criminals as the result of connection to Superman, and encounters an emerging community of metahumans, as well as people from parallel universes. She is aided by a few close friends and family who guard her secrets – most significantly her cousin's longtime friend, James Olsen (Mehcad Brooks) and tech genius Winn Schott (Jeremy Jordan).
In the second season, Kara and her allies, including her cousin Superman, deal with feuds between Earth's native populace and extraterrestrial community, and investigate conspiracies against both parties from enemies such as the shadowy organization Project Cadmus, masterminded by Lillian Luthor (Brenda Strong), mother of Superman's archenemy Lex Luthor, who later joins forces with the Cyborg Superman, Hank Henshaw (Harewood) and Supergirl's adoptive father, Jeremiah Danvers (Dean Cain). At the same time, Kara becomes friendly with Lillian's stepdaughter Lena Luthor (Katie McGrath), the new CEO of LuthorCorp, and struggles with romantic feelings for recent Earth arrival Mon-El (Chris Wood), a survivor from Krypton's neighboring planet Daxam. In other storylines, James becomes the masked streetfighting vigilante Guardian; Alex comes out as gay and begins dating Maggie Sawyer (Floriana Lima); and J'onn befriends a younger Martian, M'gann (Sharon Leal), from the White Martian race that killed his people.Melissa Benoist as Kara Zor-El / Kara Danvers / Supergirl: A 24-year-old Kryptonian living in National City, who must embrace her powers after previously hiding them. She assists her adoptive sister as part of the Department of Extra-Normal Operations (DEO) as she discovered the truth that her adoptive father also worked for the DEO so they would not take her, while Alex's co-workers at the DEO help her perfect her powers. Kara worked as Cat Grant's assistant at CatCo. Benoist expressed her excitement over portraying the character, and being able to "[tell] a story about a human being really realizing their potential and their strength". At the end of season one, Kara was promoted by Cat and became a junior reporter at the beginning of season two. Malina Weissman portrays a young Kara.
Mehcad Brooks as James Olsen / Guardian: A former Daily Planet photographer, James moved to National City and became the new art director for his former colleague, Cat Grant, at CatCo Worldwide Media. He is initially a potential love interest for Kara. Among his reasons for moving across the country include his breakup with his fiancée, Lucy Lane, and keeping an eye on the newly revealed Supergirl for Superman. While working at the Daily Planet, James received the Pulitzer Prize for taking the first photograph of Superman. In the second season, James becomes Guardian. He also becomes the acting CEO of CatCo after Cat Grant takes a leave of absence.
Chyler Leigh as Alex Danvers: Kara's adoptive sister. She is a scientist and government agent who works for Hank Henshaw at the DEO, serving as his right-hand. Having been extensively trained in combat after joining the DEO, Alex in turn provided rigorous training to Kara in order to decrease her reliance on her powers. Initially, like Kara, she becomes suspicious of the DEO and thus her own role upon learning of their father having worked there in order to protect Kara, but Alex ultimately learns that Henshaw is the Martian survivor J'onn J'onzz in shape-shifted disguise, whom her late father had rescued before his and the real Henshaw's deaths. Jordan Mazarati plays a young Alex. In season two, Alex continues to search for her father, while she meets and befriends Maggie Sawyer. She develops feelings for her, forcing Alex to confront her sexuality.
Jeremy Jordan as Winslow "Winn" Schott, Jr.: A tech expert who worked alongside Kara at CatCo, he is Kara's best friend and serves as one of her allies, helping her develop her costume and aiding her in her adventures. Winn has an unrequited feelings for Kara and is a rival with James for her affection. However, at the end of "For the Girl Who Has Everything", Winn has accepted the fact that it's best that they remain as best friends, and in "Solitude", he begins seeing Cat Grant's new assistant, who is also Kara's rival; Siobhan Smythe, who is subsequently fired by Cat and who, in "Worlds Finest", becomes a supernatural metahuman supervillain called Silver Banshee. In the series, he is the son of Toyman. Cat nicknames him Toyman Junior after she finds out. In season two, Winn left CatCo to work at the DEO as a desk agent. He also works with James Olsen as his vigilante partner.
David Harewood as J'onn J'onzz / Martian Manhunter: The head of the DEO who takes Hank Henshaw's likeness after Henshaw is killed in Peru while hunting J'onn. J'onn takes Henshaw's likeness in order to reform the DEO from within as well as to watch over Alex and Kara. The evolution of Henshaw was discussed during the filming of the pilot, with the executive producers jokingly saying that Harewood would be a good actor to play the Martian Manhunter in a potential television series, to which DC Comics' Geoff Johns asked why it could not be done in Supergirl. Harewood reflected that he had difficulty "find[ing] an angle to play Hank Henshaw" in the pilot, and became excited when he was told about the change to his character's backstory. Harewood also recurs in the series as the real Hank Henshaw, who becomes Cyborg Superman.
Calista Flockhart as Cat Grant: The shallow and superficial founder of the media conglomerate CatCo Worldwide Media, who feels, since she "branded" Kara as "Supergirl", that she has proprietary custody over the new hero. Before she founded CatCo, she was a gossip columnist at the Daily Planet, and before that, the personal assistant to the Daily Planet's Editor-in-Chief, Perry White. Cat investigates and reveals that Supergirl is Superman's cousin, which then causes Kara to become a target for some of Superman's rogues gallery. Cat also serves as a mentor to Kara, dispensing advice about being a woman in a man's world. In the episode "Hostile Takeover", she suspects that Kara is Supergirl. In the second season premiere, Cat announces she is taking a leave of absence from CatCo, leaving James to run the company in her stead.
Chris Wood as Mon-El: A superhero and prince from the planet Daxam with similar powers to Superman and Supergirl, Mon-El lands on Earth in the pod at the end of season one.
Floriana Lima as Maggie Sawyer: A detective for the National City Police Department who takes a special interest in the cases involving aliens and metahumans.
By September 2014, Warner Bros. Television was looking to create a television series centered around Supergirl. Executive producers for the series include Greg Berlanti (also a creator/producer for Arrow and The Flash), Ali Adler, who are both writing the script, and Berlanti Productions' Sarah Schechter. DC Comics' Geoff Johns is also expected to be part of the project. Titles under consideration for the series included Super and Girl. Berlanti confirmed the show shortly after, and stated it was in development and had yet to be pitched to networks. On September 20, it was announced that CBS had landed Supergirl with a series commitment, with an expected premiere in 2015 of the 2015–16 television season. In January 2015, CBS Entertainment Chairman Nina Tassler revealed the show would be a procedural, saying, "There will be [crime] cases, but what [executive producers] Ali Adler and Greg Berlanti pitched was a real series arc for her. The beauty of it is now with shows like The Good Wife and Madam Secretary, you can have serialized story elements woven into a case of the week. She's a crime solver, so she's going to have to solve a crime."
In January 2015, it was announced by The Hollywood Reporter that Melissa Benoist would star as Supergirl. Benoist later revealed that auditioning for the part "was a long, drawn-out, three-month process"; she was the first actress looked at for the role, although Claire Holt and Gemma Atkinson were also considered. In March 2015, Blake Neely, composer for Arrow and The Flash, revealed he would be composing for Supergirl. The show was officially picked up to series on May 6, 2015. It was originally set to premiere in November 2015, before being moved up to October 26, 2015. The pilot episode was screened at San Diego Comic-Con International 2015 on July 8 and 11, 2015. In July 2015, Adler spoke on how much influence Superman would have on the show, saying, "Our prototype is the way the president is seen on Veep. It's certainly [inspired by] so much of what Julia Louis-Dreyfus' character goes through. Ultimately, this is a show about Supergirl and we really want to see it through her lens." On November 30, 2015, CBS ordered an additional seven episodes of Supergirl, for a full season of 20 episodes.
On May 12, 2016, Warner Bros. Television announced that the series had been renewed for a second season of 22 episodes and would move to The CW. The season is scheduled to debut in October 2016. With the move of the production to Vancouver, it was unclear if Calista Flockhart would remain with the series, as her original contract stipulated that she work near her home in Los Angeles. The CW president Mark Pedowitz said Flockhart wanted to remain with the series and that "We're in ongoing discussions... we're happy to have her in [in whatever capacity] works out." Flockhart ultimately reached a deal to be recurring in the second season, with the production flying her to Vancouver every few weeks to film material.
The costume for Supergirl was created by Colleen Atwood, who also designed the costumes for Arrow and The Flash. Benoist stated that she is aware of the costume worn by Kara in more modern depictions of in the comics, and expressed that the "micro-mini hemline" of the skirt in the version created by Michael Turner could be "a little daunting ... but that's good. I like being pushed." Promotional photos of Benoist wearing Atwood's design were released on March 6, 2015. Atwood indicated that she wanted to "embrace the past ... but more importantly, thrust her into the street-style action hero of today." Atwood later revealed details about the costume such as the cape being fastened to an undersuit so as not to pull the costume and that the fabric used was Eurojersey. The reveal of the Martian Manhunter costume in "Human For a Day" was created through visual effects, though a physical version was created to appear in later episodes, with it proving to be one of the most challenging costumes for the costume team.
Reception of the Supergirl costume upon its reveal was mixed. Entertainment Weekly's Natalie Abrams commented that the new look of the costume looks and feels different in a good way. The new costume avoids exposing the character's midriff, as it does in the Michael Turner version of the costume from the comics, as well as having Benoist wear stockings underneath the skirt with over-the-knee boots. Abrams compared the texture of the costume to that worn by Henry Cavill as Superman in Man of Steel, as well as the positioning of the cape on the suit, and the decision to do away with the bright blue and red color scheme. Andrew Dyce, from Screen Rant, found the new costume to perfectly balance itself between classic nostalgia and modernism. The Washington Post noted that Atwood's design was successful, praising her ability to take "cartoon-y tints" and moving them to darker tones.
E! Online was less impressed with the design, negatively comparing it to a "cheap Halloween costume", with washed out colors, and not buying into the "gritty, 'street style'" look Atwood was intending. TV Guide questioned Atwood's design, and noted that although the promotional image has Benoist trying to appear as a powerful hero, the thigh-high boots and pleated skirt comes across as a "model advertising a moderately-priced Halloween costume".
In February 2015, it was announced that Andrew Kreisberg, co-creator of Arrow and The Flash, had joined the series as a writer and executive producer; and Arrow / The Flash and Smallville alum Glen Winter was announced to be directing the pilot. Principal photography for the pilot took place from March 4 to March 29, 2015. Filming locations included the Warner Bros. lot, where Lois and Clark was shot. Each episode cost approximately $3 million to broadcast, which is one of the highest license fees ever for a first year show.
The second season is being filmed in Vancouver, rather than Los Angeles where the first season was shot. This was done to reduce the high production costs of the series, one of the issues that made CBS wary to renew the series on their network.
In Canada, Supergirl aired in a sim-subbed simulcast on Global with the American broadcast in the first season; the second season saw it move to Showcase in the same arrangement.
The series premiered on October 29, 2015, in the United Kingdom on Sky One. The series premiered in Australia on December 6, 2015 on FOX8.
Review aggregation website Rotten Tomatoes gave the series premiere a 97% approval rating from critics and with an average rating of 7.6/10 based on 66 reviews. The site's consensus states: "Melissa Benoist shines as Superman's plucky little cousin in Supergirl, a family-friendly comic-book adaptation that ditches cynicism for heart." Metacritic, which uses a weighted average, assigned a score of 75 out of 100 based on reviews from 33 critics, indicating "Generally favorable reviews". Cliff Wheatley of IGN gave the pilot episode a 7/10, praising Melissa Benoist's performance as Kara and the fun take on the Superman mythos.
Rotten Tomatoes gave the premiere of the second season a 100% approval rating from critics and with an average rating of 8.3/10 based on 20 reviews. The site's consensus reads, "The arrival of the more famous cousin in Supergirl does nothing to detract from the show's lead, who continues to deliver strength, action, and relatability." Metacritic assigned a score of 81 out of 100 based on reviews from 4 critics, indicating "Universal acclaim".
In November 2014, Berlanti expressed interest in Supergirl existing in the Arrowverse, the same universe as his other series Arrow and The Flash, and in January 2015, The CW president Mark Pedowitz revealed that he was also open to a crossover between the series and networks (due to Berlanti executive producing all three and The CW being co-owned by CBS). However, CBS Entertainment chair Nina Tassler stated that month that "those two shows are on a different network. So I think we'll keep Supergirl to ourselves for a while." In August 2015, Tassler revealed that while there were no plans at the time to do crossover storylines, the three series would have crossover promotions.
Pedowitz regretted passing on the series when presented it in mid-2014, saying, "We hadn't launched The Flash yet, we weren't ready to take on another DC property. In hindsight we probably should've gone that direction...Sometimes you lose great shows." In January 2016, during the Television Critics Association press tour, he said that The CW was still interested in a crossover with Supergirl if the producers could find a way to do it, and Berlanti added that while no official conversations had taken place, internal ones had concerning how a crossover would work. He also noted that for a crossover to happen during Supergirl's first season, it would have to be figured out "in the next month or so". Glenn Geller, Tassler's successor at CBS, then stated on the matter, "I have to be really careful what I say here. Watch and wait and see what happens."
On February 3, 2016, it was announced that Grant Gustin, who appears as Barry Allen / Flash on The Flash, would appear in the eighteenth episode of the first season, "Worlds Finest". While no plot details on the episodes were released at the time, Ross A. Lincoln of Deadline.com noted that "the in-universe reason" for the crossover was due to Barry's ability to travel to various dimensions, thus implying that Supergirl exists on an alternate Earth to the Arrowverse in a multiverse. The Flash episode "Welcome to Earth-2" confirmed this, showing an image of Benoist as Supergirl during a sequence where characters travel through that multiverse. The earth that the series inhabits is Earth-38 in the Arrowverse multiverse, and has been informally referred to as "Earth-CBS" by Marc Guggenheim, one of the creators of Arrow.
During the second season, Supergirl appears in "Invasion!", a crossover episode of The Flash, Arrow and Legends of Tomorrow, when she's recruited by Barry Allen and Cisco Ramon at the end of "Medusa" to help fight off an invasion by the Dominators. Supergirl and The Flash also featured in a musical crossover, featuring several covers of existing songs along with two original numbers. Similar to "Invasion!", the crossover begins at the end of the Supergirl episode "Star-Crossed" and primarily takes place during The Flash episode "Duet", featuring the Music Meister as the antagonist. After "Invasion!", Guggenheim felt "If there's an appetite for it from the fans and from the network," the crossover next year could be "a proper four-part crossover." At the 2017 Paleyfest event, Kreisberg reiterated the creative team's intention to do a full four-way crossover the following year.
Beginning in January 2016, DC Comics launched a 13-issue, bi-weekly digital comic, Adventures of Supergirl. Written by Sterling Gates and drawn by a rotating team of artist including Bengal, Jonboy Meyers, Emanuela Lupacchino, and Emma Vieceli, the comic, while not directly tying into the show, tells stories set in the universe of the show.