Denis Buckley became part of Connacht Rugby's academy ahead of the 2009–10 season. In September 2011, while in his third year at the academy, Buckley made his first appearance for the team. His first European appearance came against Toulouse in the 2011–12 Heineken Cup in January 2012, also as a replacement. Buckley became part of Connacht's senior squad the following season and has been a mainstay ever since.