Katherine Evelyn Anita Cassidy was born on November 25, 1986, in Los Angeles, California.
She is the daughter of former pop idol David Cassidy and former model Sherry Benedon. Her paternal grandparents were the actors Jack Cassidy and Evelyn Ward.
Katie grew up in Calabasas, California, living with her mother Sherry and her stepfather Richard.
She has two older sisters named Jenna and Jamie and a younger brother called Beau.
As a child Katie became a cheerleader for the California Flyers and for Calabasas High School.
Even when she was still in elementary school Katie was already interested in show business and was allowed to take part in the community theatre.

Growing up Katie also did some modelling for brands like Abercrombie & Fitch, Rock & Republic and Guess?, but wasn’t allowed to pursue a professional acting career before she finished high school.

After graduating in 2005 Katie had plans to attend Tisch School of Performing Arts in New York, but decided to move to Los Angeles instead.
She landed a recurring part in the tv show 7th Heaven and starred in several movies including Click and the two When A Stranger Calls and Black Christmas.

In 2007 she was cast as Ruby in the CW show Supernatural.
You can currently see Katie as Trish Wellington in the new CBS series Harper’s Island.
Her future projects include a role in the 2009 remake of Melrose Place and the movie Fencewalker.

Katie was dating singer Jesse McCartney for three years and he confirmed that the songs on his latest album Departure were written about her.
Leona Lewis’ #1 hit Bleeding Love was also written by Jesse and deals with his emotions after Katie broke up with him in 2007