Archer made his 150th appearance for Munster on 1 January 2018, doing so when he came off the bench against Ulster in a 2017–18 Pro14 fixture. He signed a two-year contract extension with Munster in January 2018. Archer made his 150th United Rugby Championship appearance in Munster's 37–28 win against Italian side Benetton in round 20 of the 2018–19 season on 12 April 2019. He won his 200th cap for Munster in their 2019–20 Pro14 round 7 fixture against Edinburgh on 29 November 2019, becoming the eleventh player to achieve the accolade for the province. Archer signed a two-year contract extension with Munster in January 2020, a deal that will see him remain with the province until at least June 2022.