Katie Cassidy was first seen in the Episode: "Oh Mother, Who Art Thou?" of the American police procedural drama television series ‘The Division’ in 2003. She continued to make small appearances in television series and shows such as ‘Listen Up!,’ ‘7th Heaven’ (2005), before making her big-screen debut in the 2006 American psychological horror-thriller film ‘When a Stranger Calls’ directed by Simon West. Despite being panned by critics, the film came out as an average box office success. That same year, she portrayed ‘Kelli Presley’ in the slasher film ‘Black Christmas’ directed by Glen Morgan. The film received mixed to negative reviews from critics. In 2007, she became a part of the American dark fantasy drama television series ‘Supernatural’ created by Eric Kripke. She played the role of ‘Ruby’ and remained on the show until 2008.
In 2008, she appeared in the French English-language action-thriller film ‘Taken’ directed by Pierre Morel. The film received a mixed response from critics and was a major commercial success, earning over $226.8 million on a budget of $25 million. She next played the role of ‘Kris Fowles’ in the 2010 American slasher film ‘A Nightmare on Elm Street.’ The film saw mostly negative reviews upon release but that didn’t stop it from becoming a major box office success. Cassidy also received the ‘Teen Choice Award’ nomination for her performance in the film. In 2012, she joined the main cast of the American superhero television series ‘Arrow’ where she played the role of ‘Laurel Lance / Black Canary / Black Siren.’ The show ran for 8 seasons and went off-air in 2020. In 2015, Cassidy reprised her role as ‘Laurel Lance / Black Canary’ in the American superhero television drama series ‘The Flash.’ She remained a part of the show until 2018.
Cassidy portrayed ‘Sharon Tate’ in the 2016 American horror film ‘Wolves at the Door’ directed by John R. Leonetti. The film received mostly negative reviews from critics and holds an approval rating of 0% on Rotten Tomatoes. She was last seen in the 2021 American romantic crime drama film ‘I Love Us’ directed by Danny A. Abeckaser. Cassidy will be next seen in the upcoming Grant S. Johnson-directed American spy action-thriller film ‘Agent Game.’