O'Connor grew up in Howth, County Dublin, Ireland, until his three younger sisters, Melanie, Ella and Nicola were born.
[4] That same year, he starred as the school-bully and chief antagonist Weasel in the teen coming of age film Handsome Devil.
[7] In May 2018, it was announced that O'Connor would play Prince Harry Tudor (later Henry VIII) in the 2019 STARZ mini-series The Spanish Princess.
O'Connor played the role of Arne Cheyenne Johnson in the 2021 release of The Conjuring: The Devil Made Me Do It.
The film depicts the real life case of Johnson; the first murder defendant in American legal history to plead not guilty by reason of demonic possession.