Gaslit will follow the untold story of Martha Mitchell, a celebrity Arkansan socialite who was married to Attorney General John Mitchell.
Roberts will portray Martha Mitchell, the first person to publicly sound the alarm on President Richard Nixon's involvement in Watergate. Penn will star as John Mitchell, who will be forced to choose between Martha and the president.
Matt Ross (Captain Fantastic, 28 Hotel Rooms) is directing and executive producing. Robbie Pickering (Mr. Robot, Search Party) is serving as showrunner.
Roberts, Sam Esmail, Chad Hamilton, Gabriel Roth and Josh Levin are also executive producing with Lisa Gillan and Marisa Yeres as co-executive producers.
Gaslit is based on Slate podcast Slow Burn. Production will begin later this spring and will be produced by UCP, a division of Universal Studio Group, for Starz. Leon Neyfakh, who created the podcast, is consulting.
"I'm so happy to have the opportunity to share the heartbreaking, fascinating story of Martha Mitchell with the world," Pickering said in a statement.
"Martha was the first and loudest voice to speak out agains the bumbling criminality of a crooked presidential administration and she was one of the most complicated public martyrs of the era. To find anyone willing to tell her story is a dream. To be making it with Sam, Julia, Sean, Matt, UCP and Starz seems impossible. I'm over the moon," he continued.