Nicole Maines, a transgender actor and activist, will join the upcoming fourth season of the Warner Brothers drama as Nia Nal, who becomes known as Dreamer.
Speaking after her character was announced at Comic Con in San Diego, California, she told Variety magazine.: "It seems only fitting that we have a trans superhero for trans kids to look up to."
She added, "I want fans to take away an understanding of trans people. We can be anybody, we can be who we want, we can be superheroes - because in many ways we are."
A transgender activist who won a discrimination lawsuit after her school refused to let her use the girls’ bathroom.
The character is described as a “soulful young transgender woman” with a “fierce drive to protect others”.
Supergirl is based on the DC Comics character of the same name and is set in the same universe as other comic book characters such as The Flash and Arrow.