 Fennelly subsequently joined the Kilkenny under-21 team, winning All-Ireland medals in 2004 and 2006.By this stage he had also joined the Kilkenny senior team, making his debut during the 2006 league.Over the course of the next twelve seasons, Fennelly won eight All-Ireland medals, including a record-equalling four championships in-a-row from 2006 to 2009, followed by back-to-back triumphs in 2011 and 2012 and a final two championships in 2014 and 2015.