Harrington is perhaps best known for her role as the main character's sister in the 1993 film What's Eating Gilbert Grape. Her character was aged around 20 though the Actress herself was 35 at the time. She has also had a prominent role in the 1986 film Maximum Overdrive, written and directed by horror Novelist Stephen King, in which she played the love interest to Emilio Estevez's character.
She had a supporting role in the 1997 film The Devil's Advocate, alongside Keanu Reeves and Al Pacino. Harrington has also appeared in television series including Quantum Leap. She co-wrote the script for the film The Moon and the Sun.