Born and raised on Long Island, New York, Kelly studied music in high school and pursued a degree in drama at Marymount Manhattan College in New York. While performing in a senior-year theatrical showcase, she was spotted and soon after was signed by an agent.

She made her feature film debut in The Boy Who Cried Bitch. Her other noted film roles include Billy Bathgate, opposite Dustin Hoffman, The Cutting Edge, Twin Peaks: Fire Walk With Me, directed by David Lynch, Chaplin, with Robert Downey Jr. and director Sir Richard Attenborough and With Honors, opposite Joe Pesci and Brendan Fraser.

She also provided the voice of Nala in Disney's The Lion King. Her other film credits include Unhook the Stars, with Gena Rowlands and Marisa Tomei, and Dangerous Beauty directed by Marshall Herskovitz.Kelly's previous television appearances include the telefilms Love, Lies and Murder and Daybreak with Cuba Gooding Jr. She received critical accolades for her performance as Helen Keller in the television movie Monday After the Miracle and made her television series debut as the star of the romantic drama series To Have and To Hold.