The title is a reference to Agent 355, which was the codename of an unidentified female spy who fought for the Patriots during the American Revolution.
Marie is shown speaking English, German, and French at various points. Diane Kruger is fluent in all three languages.
Jessica Chastain proposed the idea for a female-led spy film in the same spirit as the Mission: Impossible and James Bond series to her X-Men: Dark Phoenix (2019) director Simon Kinberg while in production on that film.
Marion Cotillard was cast but dropped out of the film for personal reasons. She was replaced by Diane Kruger.
The film was the hottest-selling item in the Cannes market in May 2018. Universal Pictures paid $20 million for U.S. rights, while Huayi Bros. paid $20 million for distribution rights in China. Huayi Bros. walked away amid Bingbing Fan's tax evasion scandal, leaving the project--with a budget said to be $75 million-plus--in jeopardy.