Hilary Erhard Duff was born on September 28, 1987 in Houston, Texas, to Susan Duff (née Cobb) and Robert Erhard Duff, a partner in convenience store chain. When Hilary was six, she had been traveling in the Cechetti Ballet with her sister Haylie Duff but decided she wanted to fulfill her dream of acting. Her first starring role was when she played the young witch "Wendy" in Casper Meets Wendy (1998).

Duff became a teen idol when she starred in the #1 hit Disney Channel series Lizzie McGuire (2001).

She has also starred in the movies The Lizzie McGuire Movie (2003), Agent Cody Banks (2003), Cheaper by the Dozen (2003), A Cinderella Story (2004), Raise Your Voice (2004), The Perfect Man (2005) and Cheaper by the Dozen 2 (2005).

Additionally, Duff stormed the music charts, with singles "So Yesterday" and "Come Clean" settling nicely into the top 40. Hilary's first album, "Metamorphosis", debuted at #2 on the Billboard 200, and eventually ascended to #1 in the following weeks.

She starred in Material Girls (2006) with her sister Haylie Duff and released her fourth studio album, Dignity (2007), with Hollywood Records.

In 2015, she released her fifth studio album, Breathe In. Breathe Out. She stars as Kelsey Peters in Younger (2015).