She became known for her role as Spencer Hastings in the teen drama Pretty Little Liars alongside Ashley Benson. Her acting has earned her a Teen Choice Award and a Young Hollywood Award.
She co-starred with the Olsen twins as Kristen in the 1998 film Billboard Dad.
Her father is TV producer Donald P. Bellisario and her half-brother is actor Michael Bellisario. She began dating actor Patrick J. Adams after working with him in theater, and appeared alongside him in Pretty Little Liars and The Come Up. They married in December 2016.
She appeared in several episodes of NCIS with Mark Harmon from 2005 to 2006.