The actress is best known for her role as Marley Rose in Glee's fourth and fifth seasons.
Writing on Twitter, Benoist expressed her excitement at the news.
I wish there was a superhero emoji
— Melissa Benoist (@itsmmbenoist) January 22, 2015
But seriously, sans emoji... I AM SO EXCITED !!!!!!!!!!!!!!!!!! #Supergirl
— Melissa Benoist (@itsmmbenoist) January 22, 2015
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At the TCA press event earlier this month, CBS entertainment chairman Nina Tassler called the Warner Bros-produced show a "passion" project for the network.
"We heard the pitch and realized she embodied so many of the qualities and characteristics of the classic female heroines on the network," the network executive explained.
"It's a story and coming-of-age opportunity for us. We fell in love with the pitch."
Supergirl is being developed for CBS by Greg Berlanti, who currently produces Arrow and The Flash for The CW.
Berlanti has hinted at the possibility of a three-way crossover between the shows, given that The CW is part-owned by CBS Corporation.
"I think... like if I were watching them, I would want to see that," he admitted. "But we have to get so many things right to make a good show and so much of it is luck."
The series will also feature DC Comics characters Jimmy Olsen, Cat Grant and Toyman.
Rumoured contenders for the role of Superman's cousin Kara Zor-El before now included The Originals actress Claire Holt and Emmerdale actress Gemma Atkinson.
