Brenock O'Connor plays Olly in the HBO fantasy television series Game of Thrones, a character introduced in the show, but does not make an appearance in the books published by George R. R. Martin. The character was introduced originally as a one episode character, to further the story between the Wildlings and the Night's Watch at Castle Black, but was later kept on the show to provide more backstory surrounding the deaths of Ygritte and Jon Snow in the fourth and fifth seasons, respectively. Olly made his last appearance in the sixth-season episode "Oathbreaker", when he was hanged by a resurrected Jon Snow.
O'Connor has also appeared in several other roles, including Peter Cratchit in the BBC One series Dickensian, which premiered in December 2015.
He also starred in the British children's adventure film Young Hunters: The Beast of Bevendean.
He has appeared in a pop video with Noah and the Whale as well as several television commercials for Haribo, and as a lead character part in one episode of Holby City.
On stage O'Connor has performed in front of audiences on the tour of Cameron Mackintosh's Oliver!, playing the part of The Artful Dodger alongside Iain Fletcher, Neil Morrissey and Samantha Barks.
O’Connor had the main character as Freddie Pemberton in 2017’s British comedy series - Living the Dream. In 2018, his acting featured in The Split as Sasha which was a Minor character.
In 2020, he portrayed the role of Tom Harris in Alex Rider TV series.
In addition to acting, O'Connor is a singer and guitarist, and has posted several cover songs on YouTube.