She is known for her work in the Star Wars franchise as young Mon Mothma, having portrayed the character in Revenge of the Sith, Rogue One, and the Disney+ series Andor and Ahsoka.
[4][1] O'Reilly was cast as the understudy in director Gale Edwards' production of The White Devil a week after graduating from drama school.
[9] In 2005, O'Reilly played the young Mon Mothma in Star Wars: Episode III – Revenge of the Sith, though most of her scenes were ultimately cut.
[citation needed] In 2016, O'Reilly appeared in the British drama The Secret, for which she gained acclaim and was reported to play her character "beautifully".
[12] 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,[13] attached to the ICC team from Britain's Scotland Yard.
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.
[14] In 2015, O'Reilly starred as Dr Elishia McKellar, in an Australian paranormal drama Glitch, set in fictional small country town called Yoorana.
[citation needed] In 2005, O'Reilly moved to London with her husband, Luke Mulvihill, intending to stay for a couple of years, but were still living there in 2020.