The 22-year-old English actress, who rose to prominence playing Hermione Granger in the "Harry Potter" film series, is in discussions to play Ila, a young woman who develops a close relationship with Noah's son, Shem, who will be played by Douglas Booth, according to Deadline New York.
The young actor Logan Lerman has signed on to play Noah's other son, Ham, while the Academy Award-winner Crowe will play the title character, the man who gathers two of every animal and builds an enormous boat to continue life on Earth after an apocalyptic flood.
Watson, who has over 3 million followers on Twitter, tweeted on 22 May, "Just added @DarrenAronofsky. I love his work. P.S. don't be put off by his profile picture! : ) x."
Aronofsky, who made "Black Swan", is expected to start the shoot in July for an eventual release in March 2014.
Watson's next film, "The Perks of Being a Wallflower," is set for a limited release in September.
Being co-financed by Paramount and New Regency, "Noah" retells the biblical story of Noah and his ark as found in the book of Genesis in the Old Testament. It begins when God sees how wicked the human race has become, and decides to destroy the majority of Earth's living creatures as a result. God commands "a righteous man", Noah, to build an ark on which he, his family and two of each kind of animal can escape the impending flood that He will unleash on the Earth.
Paramount Pictures has said the $130 million film, which will begin production in Iceland and New York, will stick closely to the story presented in the Bible. However, the film is likely to focus more on environmental issues than on the spiritual implications of the story.
"I think it's really timely because it's about environmental apocalypse which is the biggest theme, for me, right now for what's going on on this planet," Aronofsky, who co-wrote the screenplay for "Noah," told SlashFilm.com in 2008. "So I think it's got these big, big themes that connect with us. Noah was the first environmentalist. He's a really interesting character."
Aronofsky added, "I don't think it's a very religious story … I think it's a great fable that's part of so many different religions and spiritual practices. I just think it's a great story that's never been on film."