Katie Cassidy is the daughter of actor David Cassidy and model Sherry Williams. She took interest in show business as a kid, leading her to appear in several local theater productions. She also dabbled in modelling while in high school. As her mother didn't allow her to act until she has taken at least some college prep courses, she didn't get her start until 2006, with the movie When A Stranger Calls. Her first major role was in the 2006 remake of the film Black Christmas.
Cassidy achieved bigger success in television, however. After recurring roles in 7th Heaven and Supernatural - where her character was recast due to budget constraints - she took a major role in the CBS miniseries Harper's Island. Her portrayal there took the attention of critics, and led to a role in the CW's reboot of Melrose Place, which tanked after only one season.
Cassidy's later roles include the films A Nightmare on Elm Street and Monaco, as well as a slot on the fourth season of Gossip Girl, where she plays the love interest to Chace Crawford's Nate.
2010: Gossip Girl (TV series) - Juliet Sharp
2010: A Nightmare on Elm Street - Kris Fowles
2009-2010: Melrose Place (TV series) - Ella Simms
2009: Harper's Island (TV series) - Trish Wellington
2007-2008: Supernatural (TV series) - Ruby/Lilith
2008: Taken - Amanda
2007: Walk the Talk - Jessie
2007: Live! - Jewel
2007: You Are Here - Apple
2006: Black Christmas - Kelli Presley
2006: Click - Samantha at 27 Years Old
2006: The Lost - Dee Dee
2006: When a Stranger Calls - Tiffany
2005: Sex, Love & Secrets (TV series) - Gabrielle
2005: 7th Heaven (TV series) - Zoe
2005: Listen Up (TV series) - Rebecca
2003: The Division (TV series) - Young CD