The "Help" star, who was set to play a scientist who develops a terrifying virus in the superhero sequel, has apologised to her fans after turning down the role, reported Aceshowbiz.
"Sorry to say that 'Iron Man 3' isn't going to work out. My schedule is jammed packed (sic) and I can't fit anything else in. The press announced my possible attachment far too soon. I know many of you wanted me to be involved, and I'm so sorry to disappoint you.
"Hopefully there'll be another Marvel film in my future. Shane Black and everyone on the IM3 team are really wonderful. I'm very excited to see the film when it comes out," Chastain posted on her Facebook page.
Iron Man 3 is due to be released next year.
