The younger sister of actress Dakota Fanning, she made her film debut as the younger version of her sister's character in the drama film I Am Sam (2001). As a child actress, she appeared in a string of films including Because of Winn-Dixie (2005), Babel (2006), Phoebe in Wonderland (2008), and Sofia Coppola's Somewhere (2010).
In 2011, Fanning starred in her breakout role as Alice Dainard in J. J. Abrams' sci-fi-drama, Super 8, for which she received positive reviews and a Spotlight Award at the Hollywood Film Festival.
In the wake of this success, she had leading roles in the films We Bought a Zoo (2011), Ginger & Rosa (2012), and Maleficent (2014), in which she portrayed Princess Aurora.
She made a transition into independent cinema with roles in films such as 3 Generations (2015), The Neon Demon (2016), 20th Century Women (2016), and The Beguiled (2017), the latter reuniting her with Coppola.