Harbour's role in the film is being kept under wraps. Production is set to begin in June in London.
Cate Shortland (Lore) is directing based off a script by Jac Schaeffer. Florence Pugh is also set to star.
Johansson has been portraying Black Widow, a highly-trained spy who hails from Russia, since 2010, when she first appeared as the character in Iron Man 2. The actress has reprised the role in a number of Marvel films such as the Avengers series including Infinity War, the upcoming End Game and two Captain America films.Black Widow will be the second Marvel film led by a female superhero following the recently released Captain Marvel starring Brie Larson. Black Widow will reportedly take place before the events of the first Avengers film.
Harbour, in addition to appearing in Stranger Things Season 3 which arrives on Netflix on July 4, will also be seen as the title character in Hellboy, set to arrive in theaters on April 12.