The mother-of-three announced her latest gig in a post on her Instagram page as she shared a snap of herself in bed reading a script and wrote alongside it, "studying @hesallthatmovie."
Addison then commented on Kourtney's post, writing, "worrkkkkkkk."
Following the Instagram interaction, the "He's All That" official account reshared Kourtney's picture on their page, and revealed the reality star's character name in the movie.
"Introducing Jessica Miles Torres #HesAllThat," they wrote.
The pair will appear alongside "Cobra Kai" star Tanner Buchanan in the gender-bending remake of Rachael Leigh Cook's 1999 classic "She's All That".
R. Lee Fleming, the screenwriter behind the original, is working on the remake, in which Rae will play a popular high schooler, who takes on a challenge to turn a loser into a prom king.
"He's All That" won't be Kourtney's first acting role - she made her acting debut on soap opera "One Life to Live" in 2011.
Kourtney's casting news comes as her family reality TV show "Keeping Up with the Kardashians" is coming to an end.
As the ratings are declining, the show will not return to TV after the current season concludes.
The matriarch and momager Kris Jenner blamed social media for the 'KUWTK" ending. "When we first started, there was no Instagram or Snapchat or other social media platforms," she claimed. "The world has changed. Now there are so many, the viewer doesn't have to wait three or four months to see an episode. We can give them all of the information anyone would ever want to know in real time."
Rumor has it, the family are eying to take the show to streaming service after being abandoned by E!.