Garner was born in Houston, Texas and raised in Charleston, West Virginia. She studied ballet for nine years before enrolling as a chemistry major at Denison University. After realizing that she loved the stage more than science, she changed her major to drama.
She currently stars as the character of Sydney Bristow in the TV show Alias. In 2003 her marriage to Scott Foley ended and she began dating her Alias co-star Michael Vartan. She enjoys cooking, gardening, hiking, and kickboxing (a hobby inspired by her character on Alias).