Became an Oscar nominee at age fourteen for her role in the 2010 film True Grit. In 2015, she appeared in Pitch Perfect 2 and in 2016, she starred in The Edge of Seventeen. Also a singer, she released her debut EP Haiz, featuring the single "Love Myself," in 2015.
She began acting in short films at the age of eight. She was homeschooled from age 11 through high school.
In 2013, she starred as Juliet Capulet in Romeo and Juliet and played Petra in Ender's Game. She appeared in Taylor Swift's music video for "Bad Blood" in 2015.
Her parents are Cheri and Peter Steinfeld and she has an older brother named Griffin. She began dating Niall Horan in 2018. She previously dated Cameron Smoller in 2017.
She starred alongside Matt Damon and Jeff Bridges in True Grit.