She began her career in Atlanta doing commercials, working steadily in national spots for companies like McDonald's, Six Flags Amusement Parks and Oreo cookies. When Hannigan was 11, she moved to Los Angeles in hopes of breaking into film and television.
Her breakthrough role came when she was cast as Dan Aykroyd's misunderstood daughter in the feature film "My Stepmother Is an Alien." She went on to guest star on a number of popular television shows, including "Picket Fences," "Roseanne" and "Touched by an Angel." She was a recurring guest star on the series "Almost Home" and a series regular on "Free Sprit."
In her free time, the Washington, D.C. native, who has a small, dolphin tattoo on her ankle, and Dr. Seuss fan likes to surf the web, practice kick-boxing and spend time with her dogs and cats. She currently resides in Los Angeles.