Melissa Chessington Leo (born September 14, 1960) is an American actress. She is the recipient of several accolades, including an Academy Award, a Primetime Emmy Award, a Golden Globe Award, two Critics' Choice Awards, and a Screen Actors Guild Award.

After appearing on several television shows and films in the 1980s, Leo became a regular on the television shows All My Children, for which she was nominated for a Daytime Emmy Award, and The Young Riders. Her breakthrough role came in 1993 as detective and later sergeant Kay Howard on the television series Homicide: Life on the Street (1993–1997).

Leo received critical acclaim for her performance as Ray Eddy in the 2008 film Frozen River, earning her several nominations and awards, including an Academy Award nomination for Best Actress. In 2010, Leo won several awards for her performance as Alice Eklund-Ward in the film The Fighter, including the Academy Award for Best Supporting Actress.

In 2013, she won a Primetime Emmy Award for her guest role on the television series Louie. She starred in the 2015 Fox event series Wayward Pines as Nurse Pam. She then starred in the 2017 Netflix film The Most Hated Woman in America as American Atheists founder Madalyn Murray O'Hair.