Marilyn Castonguay is a Canadian film and television actress, best known for her performance in the 2012 film L'Affaire Dumont. A graduate of the National Theatre School of Canada, her performance in L'Affaire Dumont garnered a nomination for Best Actress at the 1st Canadian Screen Awards.

She has also appeared in the films Louis Cyr and Vol de nuit, and the television series Vertige, Adam & Ève and Fatale-Station.