WB had no comment.
She joins Gal Gadot, who plays the superhero; Chris Pine, who portrays Steve Trevor; Danny Huston, Robin Wright, David Thewlis and Ewen Bremner. Pine recently said the movie is set during World War I.
Patty Jenkins will direct the film, which will be released on June 23, 2017.
Charles Roven is exec producing the DC Comics tentpole for Atlas Entertainment. Zack Snyder, director of “Batman v Superman: Dawn of Justice,” is also producing.
The studio had originally sought Nicole Kidman for the role, but scheduling conflicts with her HBO show “Big Little Lies” forced her to pass on the project. Rumors had recently circulated about Wright’s role being rewritten to Hippolyta, but the studio kept Wright on as Diana’s aunt and cast Nielsen instead as her mother.
Nielsen’s recent credits include a stint on the Kevin Bacon crime drama “The Following,” as well as “The Good Wife.” She also appeared in “Nymphomaniac: Volume I.”
Nielsen is repped by UTA, Lasher Group and Lichter Adler. The Hollywood Reporter first reported the news.