Duff's mother encouraged Hilary to take up acting classes alongside her elder sister which resulted in both girls winning roles in various local theatre productions.The siblings became more enthusiastic about the idea of choosing acting as a profession, and eventually relocated to California with their mother, while their father resides at the family home in Houston to take care of their business.Duff's first role in a theatrical motion picture was in Human Nature (2002), an independent film shot around the time of the start of Lizzie Mc Guire.
The same year, Duff recorded a cover version of Brooke Mc Clymont's "I Can't Wait" for the Lizzie Mc Guire soundtrack, and "The Tiki Tiki Tiki Room" for the first Disney Mania compilation album.
Her first album was Santa Claus Lane (2002), a collection of Christmas songs that included duets with her sister Haylie, Lil' Romeo, and Christina Milian. In 2003, Duff received her first major role in a feature film when she was cast alongside Frankie Muniz in Agent Cody Banks.
In November 2008, she released a compilation of her greatest hits, Best of Hilary Duff, whose single "Reach Out" became her third #1 on the Billboard Hot Dance Club Play.
Duff has also branched into fashion by launching her own clothing lines, Stuff by Hilary Duff and Femme for DKNY Jeans, and two exclusive perfume collections with Elizabeth Arden.
However, the plans failed because Duff's representatives said she was not being paid enough for the proposed series.