 While still a member of the under-21 team, Fennelly was added to the Kilkenny senior panel in 2006.He made his debut during the National Hurling League, and subsequently collected his first winners' medal following a 3–11 to 0–14 victory over Limerick.On 2 July 2006 he made his senior championship debut in a facile 1–23 to 2–12 provincial final defeat of Wexford.