The Academy Award-nominated actress - who rose to fame as a result of roles in films such as The Help and The Tree of Life - is said to have returned to negotations, according to Deadline.
> Scarlett Johansson to reprise Black Widow role in 'Iron Man 3'?
Chastain was offered a leading role playing a scientist billed as a match for protagonist Tony Stark (Robert Downey Jr), the publication reports. However, she reportedly declined due to scheduling concerns.
She is currently working on Katherine Bigelow's Osama Bin Laden movie Zero Dark Thirty and is also attached to star alongside Joel Edgerton in double feature The Disappearance of Eleanor Rigby.
However, the filming schedules for both projects are now said to have been worked out.
Chastain was recently named one of Time magazine's 100 most influential people of the year.
Downey Jr will next play Tony Stark/Iron Man in The Avengers, released on April 26 in the UK (under the title Marvel Avengers Assemble) and May 4 in the US.
> 'Iron Man 3': Guy Pearce in final talks to play Aldrich Killian
Watch the Avengers UK press conference interviews in full below: