Hewitt began her career as a child actress and singer, appearing in national television commercials before joining the cast of the Disney Channel series Kids Incorporated (1989–1991).
She had her breakthrough as Sarah Reeves Merrin in the Fox teen drama Party of Five (1995–1999) and rose to fame as a teen star for her role as Julie James in the horror films I Know What You Did Last Summer ( 1997) and its 1998 sequel, as well as her role as Amanda Beckett in the teen comedy Can’t Hardly Wait (1998).
