Tisdale was born in Monmouth County, New Jersey on July 2, 1985, to Lisa (née Morris) and Mike Tisdale. She grew up there in Ocean Township. Her elder sister Jennifer Tisdale is also an actress. Tisdale is Jewish and her maternal grandfather is Arnold Morris, the developer of Ginsu Knives; and through her grandfather, she is also related to businessman Ron Popeil.
She was discovered by Bill Perlman, her current manager, at South Shores Mall, when she was three. At the age of eight, she received a leading role in the Broadway musical, Les Misérables and later toured internationally with the cast of Annie. She began acting, appearing in stage productions of Gypsy: A Musical Fable and The Sound of Music at the Jewish Community Center of Monmouth County.