Panettiere was born on August 21, 1989 in Palisades, New York to Skip Panettiere and Leslie Vogel. She has one younger brother, fellow actor Jansen Panettiere.

Hayden began appearing in commercials at 11 months old, first appearing in an advertisement for Playskool Toy Train. She later landed a role as Sarah Roberts on the ABC soap opera One Life to Live (1994- 1997) and later as the child Lizzie Spaulding on the CBS soap opera Guiding Light when she was eight years old (1997 - 2001). In Guiding Light, for Hayden's character Lizzie's battle with leukemia, the show received a Special Recognition Award from the Leukemia and Lymphoma Society for bringing national awareness of the disease to the attention of daytime viewers.

She has appeared in over a dozen full-length feature films, as well as several made-for-TV movies. In addition, she had a leading role as the voice of Kairi in the highly successful Kingdom Hearts series of video games for the Playstation 2. She had a starring role in FOX's Ally McBeal as Ally McBeal's daughter and a recurring guest role in Malcolm in the Middle. She guest starred in Law & Order: SVU. She played Sheryl Yoast in the film Remember the Titans. She starred in Bring It On: All or Nothing. She has a younger brother, Jansen Panettiere, who acts in the movie The Last Day of Summer.

Panettiere currently stars as Claire Bennet in the NBC series Heroes as a high school cheerleader with regenerative healing powers. Due to her role on Heroes, she has become a regular on the science fiction convention circuit, having been invited to attend many popular conventions around the world in 2007, including New York Comic-Con and Fan Expo Canada.

She will later appear in the drama film Fireflies in the Garden as a younger version of Emily Watson's character Jane Lawrence. Coincidentally, George Newbern, who played Sephiroth in Kingdom Hearts II alongside Panettiere, will also appear in the film.

In June 2007, she signed with the William Morris Agency to represent her in her endeavors. She was previously represented by United Talent Agency.

Forbes estimated that she received $2 million dollars in 2007.

Panettiere was nominated for a Grammy in 1999 for Best Spoken Word Album for Children for A Bug's Life Read-Along [2000].

She is currently working on her debut album, which was originally planned for release on May 8, 2007. The album, however, has been pushed back several times. It was first pushed back until August, then to December. Entertainment Weekly later confirmed that the album would now be released in 2008.

Neutrogena made her the cover girl for their new worldwide ad campaign; following in the footsteps of actresses Josie Bissett, Jennifer Love Hewitt, Mandy Moore, Kristin Kreuk, Mischa Barton, Gabrielle Union and Jennifer Freeman.