She made her film debut at the age of nine in the film North. In 1997, she played Molly Pruitt in the movie Home Alone 3.
She received a Toronto Film Critics Association Award for Best Supporting Actress for her role in the 2001 independent comedy Ghost World.
Her twin brother's name is Hunter. She was married to Ryan Reynolds from September 2008 until July of 2011. She then married Romain Dauriac in 2014. She and Dauriac had a daughter named Rose together, then separated in 2016. In July 2017, she began dating comedian Colin Jost. She and Jost got married in October 2020. In August 2021, the couple welcomed their first child together, a son named Cosmo.