McCarthy joined Leinster's provincial rivals Munster on a two-year contract after the completion of the 2018–19 season, and made his competitive debut for the province in their opening 2019–20 Pro14 39–9 win against Welsh side Dragons on 28 September 2019. His final appearance for the province was in their 54–11 away win against Zebre in round 6 of the Pro14 Rainbow Cup on 11 June 2021.