Fallon's career began as a visual effects coordinator with Star Wars: Episode II Attack of the Clones (2002, George Lucas), working for ILM. She continued her career in other visual effect movies such as Terminator 3: rise of the Machines (2003, Jonathan Mostow) and Van Helsing (2004, Stephen Sommers).
Then, Fallon returned to the Star Wars saga to be one of the visual effects coordinator of Star Wars: Episode III Revenge of the Sith (2005, George Lucas). She also became an actress for that movie and also appeared in the DVD extra Within a Minute: The Making of Episode III.
From Episode I to Episode II, George Lucas had tried to recast the roles of background Jedi with different actors whenever the original ones were unavailable, such as with characters Eeth Koth and Adi Gallia, but the new actors in disguise were different enough to became new characters (respectively, Agen Kolar and Stass Allie). After this, Lucas decided that, if an actor portraying a Jedi was unavailable for Episode III, that Jedi would be replaced with a new character. Stass Allie's actress, Lily Nyamwasa, returned to replay her role, but she was unavailable for pick-up shots. Lucas thus replaced Nyamwasa with Tace Bayliss for the Council scenes, and with visual effects coordinator Nina Fallon for her death scene on Saleucami (although Nyamwasa is still the canon representation of the character, appearing in reference books and action figures).
Fallon had continued her career as visual effects coordinator with Mission: Impossible III (2006, J.J. Abrams). Her following premiére took place with long-awaited 300 (2006, Zack Snyder), based on Frank Miller's adaptation of the Battle of Thermopylae, where she was the visual effects line producer. She has continued in this job with Canadian films Nitro (2007, Alain Desrochers), Continental, a Film Without Guns (2007, Stéphane LaFleur) and C'est pas moi, je le jure!(2008, Philippe Falardeu).