Archer made his Munster debut as a replacement against
Edinburgh during a
Celtic League fixture on 23 October 2009. He was part of the historic Munster team that beat
Australia 15–6 at
Thomond Park on 16 November 2010. He made his
Heineken Cup debut as a replacement in Munster's Round 5 26–10 win against
Castres on 14 January 2012, during the
2011–12 Heineken Cup. Archer was part of the team that defeated newly crowned Heineken Cup champions, and arch-rivals,
Leinster 19–9 in the
2011 Magners League Grand Final on 28 May 2011. With Munster A, Archer won the
2011–12 British and Irish Cup. He scored his first try for Munster in a
2011–12 Pro12 league fixture against
Ulster on 5 May 2012. He signed a two-year contract extension with Munster in January 2013. In October 2015, Archer was ruled out for a number of months after sustaining a neck injury that required surgery. 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, and signed a one-year contract extension in January 2022. He won his 50th Champions Cup cap for Munster in their 26–10 home win against English club
Exeter Chiefs in the second leg of their
2021–22 Champions Cup round of 16 clash on 16 April 2022, and he overtook
Billy Holland to become the second most capped Munster player of all-time when he won his 248th cap for the province in their 36–17 away defeat against
Ulster in the quarter-finals of the
2021–22 United Rugby Championship on 3 June 2022. Archer earned his 250th cap for Munster in their
2022–23 United Rugby Championship round three fixture against Italian side
Zebre Parma on 1 October 2022, coming in as a replacement for
Keynan Knox. Archer signed a one-year contract extension with Munster in February 2023, and started in Munster's 19–14 win against the
Stormers in the
final of the
2022–23 United Rugby Championship on 27 May 2023. In April 2025, Archer confirmed that he would be retiring at the end of the
2024–25 Munster Rugby season and played his final game for Munster on 31 May in the defeat to the
Sharks in the Quarter-final of the
2024–25 United Rugby Championship. He retired as Munster’s most-capped player. ==Ireland==