Katie was born into a family who knows a thing or two about entertainment and glamour. She probably got her acting gene from her paternal grandparents who were both actors and her singing prowess from her dad David Cassidy. She grew up with her mom and stepdad in Calabasas, California. Katie started off with acting in community theater productions and did some modeling with Abercrombie and Fitch. Her plan was to attend NYU Tisch School of Performing Arts, but several acting jobs came her way. She made her: More television debut in the year 2003 in the TV series The Division. From then on, she has appeared in numerous TV and film projects. In 2007, she was cast as a regular in CW action thriller Supernatural.

During her free time, Katie loves to travel and take road trips. She is also into sports such as skiing, snowboarding, soccer, and football. She likes cooking, especially making desserts. When she is not working, she likes to shop on Melrose with her sisters, Jenna and Jaime. She does not like to read much and likes to spend time on the beach.