In 2003 Walsh became a regular member of the starting fifteen during Kilkenny's successful run to the final of the National Hurling League. Kilkenny came back from eight points down to secure a stunning 5–14 to 5–13 extra-time defeat of Tipperary, with Walsh collecting his first league medal. He later made his senior championship debut on 7 June 2003 in a 3–16 to 0–10 Leinster semi-final defeat of Dublin. Walsh went on to collect his first Leinster medal on the field of play, as Kilkenny defeated Wexford by 2–23 to 2–12. The subsequent All-Ireland final on 14 September 2003 saw Kilkenny face Cork for the first time in four years. Both teams remained level for much of the game, exchanging tit-for-tat scores. A Setanta Ó hAilpín goal gave Cork the advantage, however, a Martin Comerford goal five minutes from the end settled the game as Kilkenny went on to win by 1–14 to 1–11. It was Walsh's first All-Ireland medal on the field of play. He was later honoured with his first All-Star award.