Horgan made his Munster debut against
Connacht in August 1997. He started for Munster in their first
Heineken Cup final against
Northampton Saints in May 2000.Horgan was also selected to start the 2002 Heineken Cup final loss against Leicester but broke his hand the night before in a captains run. Due to his withdrawal John O'Neill started in his place He was part of the Munster team that beat
Neath to win the
2002–03 Celtic League, and he picked up more silverware when Munster beat
Scarlets to win the Celtic Cup in May 2005. Horgan started for Munster as they beat
Biarritz 23-19 to win their first Heineken Cup final in May 2006. He played his last game for Munster on 15 May 2009 in 36-10
Celtic League win over the
Ospreys at
Thomond Park, where the team also received the trophy as
2008–09 Celtic League winners. Horgan scored Munster's final try, to the delight of the home crowd. Horgan was Munster's all-time leading try scorer, with 41 tries to his name when he retired in May 2009, until
Simon Zebo broke that record in March 2016. ==Ireland==