| Year | Award | Category | Nominated work | Result | Ref. |
| 1993 | Young Artist Awards | Best Young Actress in a New Television Series | Swans Crossing | Nominated | |
| Best Young Actress in an Off-Primetime Series | Nominated | |
| 1994 | Daytime Emmy Awards | Outstanding Younger Actress in a Drama Series | All My Children | Nominated | |
| Young Artist Awards | Best Youth Actress in a Soap Opera | Nominated | |
| 1995 | Daytime Emmy Awards | Outstanding Younger Actress in a Drama Series | Won | |
| Young Artist Awards | Best Performance by a Youth Actress in a Daytime Series | Nominated | |
| 1998 | Blockbuster Entertainment Awards | Favorite Supporting Actress – Horror | I Know What You Did Last Summer | Won | |
| MTV Movie Awards | Best Breakthrough Performance | Nominated | |
| Saturn Awards | Best Actress on Television | Buffy the Vampire Slayer | Nominated | |
| 1999 | Kids' Choice Awards | Favorite Television Actress | Nominated | |
| Saturn Awards | Best Genre Television Actress | Won | |
| Teen Choice Awards | Choice Movie Villain | Cruel Intentions | Won | |
| Choice Television Actress | Buffy the Vampire Slayer | Won | |
| Young Artist Awards | Best Performance in a Television Series (Comedy or Drama) – Leading Young Actress | Nominated | |
| 2000 | Kids' Choice Awards | Favorite Television Friends (shared with David Boreanaz) | Nominated | |
| MTV Movie Awards | Best Kiss (shared with Selma Blair) | Cruel Intentions | Won | |
| Best Performance – Female | Won | |
| Best Villain | Nominated | |
| Saturn Awards | Best Actress on Television | Buffy the Vampire Slayer | Nominated | |
| Teen Choice Awards | Choice Television Actress | Won | |
| 2001 | Golden Globe Awards | Best Performance by an Actress in a Television Series – Drama | Nominated | |
| Kids' Choice Awards | Favorite Television Actress | Nominated | |
| Saturn Awards | Best Actress on Television | Nominated | |
| Teen Choice Awards | Choice Television Actress | Nominated | |
| Extraordinary Achievement Award | Won | |
| Television Critics Association Awards | Individual Achievement in Drama | Nominated | |
| 2002 | Kids' Choice Awards | Favorite Female Butt Kicker | Won | |
| Saturn Awards | Best Actress in a Television Series | Nominated | |
| SFX Awards | Best Television Actress | Won | |
| Teen Choice Awards | Choice Movie: Chemistry (shared with Freddie Prinze Jr.) | Scooby-Doo | Nominated | |
| Choice Movie Actress – Comedy | Won | |
| Choice Television Actress – Drama | Buffy the Vampire Slayer | Won | |
| Young Hollywood Awards | Hottest, Coolest Young Veteran – Female | Won | |
| 2003 | Kids' Choice Awards | Favorite Female Butt Kicker | Nominated | |
| Satellite Awards | Best Actress – Television Series Drama | Nominated | |
| Saturn Awards | Best Actress in a Television Series | Nominated | |
| Teen Choice Awards | Choice Television Actress – Drama | Won | |
| 2004 | Saturn Awards | Best Actress in a Television Series | Nominated | |
| SFX Awards | Best Television Actress | Won | |
| 2005 | MTV Movie Awards | Best Frightened Performance | The Grudge | Nominated | |
| Teen Choice Awards | Choice Movie Actress – Thriller | Nominated | |
| 2011 | Virgin Media TV Award (United Kingdom) | Best Actress | Ringer | Nominated | |
| EW Entertainers of the Year | Favorite Television Actress | Nominated | |
| 2012 | Teen Choice Awards | Choice Television Actress – Drama | Nominated | |
| Zap2it Awards | Best Actor Playing Two Characters on One Show | Nominated | |
| E! Golden Remotes Awards | Star You'll Miss The Most | Won | |
| 2014 | People's Choice Awards | Favorite Actress in a New Television Series | The Crazy Ones | Won | |
| 2022 | Online Film and Television Association | Television Hall of Fame | Buffy the Vampire Slayer | Won | |
| 2023 | Savannah College of Art and Design TVfest | Icon Award | — | Won | |