While the character is a late addition to the film, Smulders is believed to be director Joss Whedon's first choice for the part, according to Deadline.
Earlier this week Samuel L. Jackson, who will play S.H.I.E.L.D. Director Nick Fury in the film, revealed that his character would be accompanied by a female sidekick who was currently being auditioned.
This sidekick is widely expected to be that of Deputy Director Maria Hill, who emerged in the comics as a cold and ruthless replacement for Nick Fury during the Civil War event.
If negotiations go to plan, a deal is expected to be signed with Smulders within the next few weeks.
Production on The Avengers is due to begin this April, followed by an announced release date of May 4, 2012.