She will be playing the character of Anna, a lone female survivor that Smith's character, Robert Neville, will come across.
We have contacted Gabrielle Union's agency UTA for confirmation, but they would not comment at this time.
The only other character of any substance in the film is Ethan. This role has also been cast with a relatively unknown actor.
Directed by Francis Lawrence, of Constantine fame, I Am Legend is expected to be released in 2007. Long in development, this project was attached to Arnold Schwarzenegger and Ridley Scott back in the '90s, thank God that didn't happen.
Synopsis: In a post-apocalyptic New York, Robert Neville fights to survive against a horde of vampire-like beings created when a medical treatment goes awry.
By day, he is the hunter, stalking the sleeping undead through the abandoned ruins of civilization. By night, he barricades himself in his home and prays for the dawn.
How long can one man survive in a world full of vampires?
Based on the Richard Matheson book by the same name I Am Legend.