On 16 January 2016, O'Connor made his competitive debut for Munster when he came on as a substitute against Stade Français in a 2015–16 European Rugby Champions Cup fixture. O'Connor made his first start for Munster on 1 September 2017, doing so in the sides opening fixture of the 2017–18 Pro14 against Benetton. He signed a two-year senior contract with Munster in January 2018. O'Connor was nominated for the 2018 John McCarthy Award for Academy Player of the Year in April 2018. O'Connor made his return from a knee injury sustained during Munster's game against Ospreys in December 2017 in their fixture against Dragons on 26 January 2019. He signed a two-year contract extension with Munster in January 2020, a deal that will see O'Connor remain with the province until at least June 2022.