Sage was born and raised in Los Angeles, California. She has a younger brother and a younger sister. Sage is Jewish. She rode horses competitively, and was the editor of her high school's newspaper.
Sage's career was launched in 2011, when she was cast in the role of Grace on the Nickelodeon series How to Rock, which first aired on February 4, 2012, and ran for a single 25-episode season. She has also guest starred on Nickelodeon's Victorious and Bucket & Skinner's Epic Adventures. In February 2013, Sage was cast in the short-lived NBC television thriller series Crisis, playing Amber, the daughter of Gillian Anderson's character. In 2016 she was cast in a starring role as Alara Kitan on the science-fiction dramedy series The Orville, which premiered on Fox on September 10, 2017. It was reported in January 2019 that Sage had left the cast of The Orville after the episode "Home", though her departure was considered open-ended for a possible return in the future.
Sage appeared as Brianna in the 2012 teen drama The First Time. In 2013, she appeared in the films The Bling Ring, Grown Ups 2 and Poker Night. She had a role in the 2014 film Neighbors, playing Zac Efron character's girlfriend Brooke Shy. Sage was a nominee for the MTV Movie Award "Best Kiss" for her onscreen kiss with Rose Byrne in Neighbors.

Return to Halston Sage Autograph Profile