• Brec Bassinger as Courtney Whitmore / Stargirl:
A high school sophomore who discovers a powerful cosmic staff and becomes the hero Stargirl. She is the leader of the new Justice Society of America. Bassinger did not look at the previous portrayals of the character by Britt Irvin on Smallville or Sarah Grey on Legends of Tomorrow because they were depicted as "older, more mature version[s]" of Stargirl. Bassinger added the series followed the comic Stars and S.T.R.I.P.E. more "in that she's young, high school, naive, which I wanted to bring that into this version of Stargirl."
• Yvette Monreal as Yolanda Montez / Wildcat:
One of Courtney's friends who becomes a member of the new Justice Society of America.
• Anjelika Washington as Beth Chapel / Doctor Mid-Nite:
One of Courtney's friends who becomes a member of the new Justice Society of America.
• Cameron Gellman as Rick Tyler / Hourman:
One of Courtney's friends who becomes a member of the new Justice Society of America.
• Trae Romano as Mike Dugan:
Pat Dugan's son and Courtney's stepbrother.
• Jake Austin Walker as Henry King Jr.:
The son of Brainwave and a student at Blue Valley High.
• Hunter Sansone as Cameron.
A student at Blue Valley High.
• Meg DeLacy as Cindy Burman.
The daughter of Dragon King and the most popular student at Blue Valley High who is determined to follow in her father's footsteps.
• Neil Jackson as Jordan Mahkent / Icicle.
A member of the Injustice Society.
• Christopher James Baker as Henry King Sr. / Brainwave.
A member of the Injustice Society.

Teenager Courtney Whitmore joins the Justice Society of America. Based on the character from DC Comics.SourceIMDB