Facinelli, 41, will play the iconic DC Comics character Maxwell Lord, said The Hollywood Reporter.
The show is based on the DC Comics character Supergirl (Kara Zor-El), who is the biological cousin to Superman and one of the last surviving Kryptonians.
Facinelli will play Maxwell Lord, a green tech billionaire who is fascinated with National City's newest citizen, Supergirl (Melissa Benoist).
In comic book lore, Maxwell Lord has wavered between being a good guy and a bad guy.
"Supergirl" centres on Superman's cousin Kara Zor-El, who comes to embrace her Kryptonian roots and becomes the hero she was destined to be.