Holt was born in Brisbane, Queensland, Australia. She graduated from Stuartholme School in Toowong at the end of 2005. She is involved in several sports: swimming, volleyball, water polo, and Tae-Kwon-Do, in which she has a black belt. When she was younger, she was in the school choir.
In addition to television and film roles, Holt has appeared in advertisements for Dreamworld, Sizzler, and Queensland Lifesaving. BuddyTV ranked her number 55 on its TV's 100 Sexiest Women of 2011 list.
In August 2011, Holt was confirmed to be in the TV series The Vampire Diaries as Rebekah. On 13 January 2013, The CW announced that Holt had joined the cast for the backdoor pilot of The Vampire Diaries spin-off The Originals, where she reprised her role as Rebekah Mikaelson. She exited the show as a series regular in the sixteenth episode of the first season, which aired in the U.S. on 11 March 2014. Holt returned as Rebekah Mikaelson in the season one finale on 13 May 2014. She continued to guest star throughout the second season of The Originals and is expected to appear again in the third.
In 2015, Holt was linked to CBS' Supergirl although she chose not pursue it. She currently stars in NBC 'event series' Aquarius as Charmain Tully.
Holt at the Ian Somerhalder Foundation's Influence Affair Red Carpet 2012