Davis said she's met Obama but has no idea if the former first lady knows about her taking on the role.
"I'm terrified. I'm absolutely terrified," Davis said. "I don't care what else I've done in my life -- I've won an Emmy, I've won an Oscar, two Tonys -- but if I mess this up, this is going to be a defining moment in my life."
"It's like, 'You raised a great kid, but you messed up Michelle Obama,'" she jokingly added.
Davis said, however, that she's confident about the script, written by author Aaron Cooley. Davis and Cooley will also executive produce the show.
"It's going to be a great script, I promise," Davis said. "Listen, I don't want to make my people mad."
"I had to wear a fat suit," Davis told host Jimmy Kimmel. "I loved it. I told them that I wanted really, really big [expletive]. I wanted to look like the women I grew up with."
Davis plays Annalise Keating on the ABC series How to Get Away with Murder, which premiered its sixth and final season Thursday.