O'Connor was born in Wantage, at the time part of Berkshire, England, to a pianist mother and nuclear physicist father;[citation needed] her family moved to Perth, Western Australia, when she was two years old.

In 2002, she starred alongside Rupert Everett, Colin Firth and Judi Dench in the romantic comedy-drama The Importance of Being Earnest, directed by Oliver Parker and based on Oscar Wilde's classic play.

[10][11] In 2004, O'Connor returned to independent films and starred in Book of Love opposite Simon Baker, and Iron Jawed Angels with Hilary Swank, Julia Ormond and Anjelica Huston.

In 2008, she starred in the short-lived ABC comedy-drama series Cashmere Mafia alongside Lucy Liu, Miranda Otto and Bonnie Somerville.

She later appeared in Jayne Mansfield's Car, Little Red Wagon and The Truth About Emanuel; and received two more AACTA Award for Best Actress nominations for Three Dollars (2005) and The Hunter (2011).

[18] In 2016, O'Connor co-starred in the horror film The Conjuring 2, alongside Vera Farmiga and Patrick Wilson,[19] and in Cleverman, opposite Iain Glen.