Larkin made his debut on the inter-county scene at the age of seventeen when he was picked for the Kilkenny minor panel. He was an unused substitute throughout the 2002 championship but collected a set of All-Ireland and Leinster medals as a member of the starting fifteen. Larkin later enjoyed a successful two-year tenure with the Kilkenny under-21 team, winning an All-Ireland medal in 2005 as well as back to back Leinster medals. He made his senior debut during the 2005 league. Over the course of the next twelve seasons, Larkin 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. The All-Ireland-winning captain of 2012, he was denied a ninth All-Ireland medal in September 2016 in what was his last game for Kilkenny. Larkin also won ten Leinster medals, six National Hurling League medals and was named All-Star, Texaco and GPA Hurler of the Year in 2008. He announced his retirement from inter-county hurling on 2 December 2016.