Television
In television, O'Reilly's first appearance was in 2001 in the Canadian television series BeastMaster as a guest star in "Slayer's Return". The following year O'Reilly appeared in Young Lions as Kimberly Oswald in the episode "Asylum Seekers". O'Reilly then appeared as a prominent character in All Saints from 2002 to 2005 as Leanne Curtis.{ Since moving to the UK, O'Reilly starred in the political mini-series The State Within, (first episode 2 November 2006) played Princess Diana in the 2007 television docudrama Diana: Last Days of a Princess, and had the lead role in The Time of Your Life (summer 2007). In 2009, she played CIA liaison officer Sarah Caulfield in the eighth series of BBC drama Spooks. She played Julie Rees in Harbinger, the two-part, season 9-opening episodes of Waking the Dead. O'Reilly also played the character of Michelle Beadley in the remake of The Day of the Triffids that aired on BBC One in December 2009.
From 2011 to 2014, O'Reilly appeared in the series Episodes as a recurring character alongside Matt LeBlanc. In June 2013, O'Reilly appeared in the pilot episode of the international crime drama Crossing Lines cast as detective and interrogation specialist Sienna Pride, attached to the ICC team from Britain's Scotland Yard. Later in 2014, O'Reilly appeared in the television mini series The Honourable Woman as Frances Pirsig. In 2015, O'Reilly appeared in the BBC television series Banished as Mary Johnson.
In early 2015, O'Reilly starred as Mary Johnson in Jimmy McGovern's Banished, a television drama focusing on British convicts in an Australian penal colony. In 2015, O'Reilly also starred as Dr Elishia McKellar, in an Australian paranormal drama Glitch. In 2016, O'Reilly appeared in the British drama The Secret, for which she gained acclaim and was reported to play her character "beautifully".
In 2017, she was cast alongside Tim Roth as Angela Worth, in the British TV Series Tin Star
