Mulcahy made his senior debut for Cork in their opening championship game against Kerry in 2000. He remained on the periphery of the team until 2003 when he secured a regular place on the starting fifteen. He won his second Munster medal that year following a 3-16 to 3-12 defeat of Waterford. Cork later reached the All-Ireland decider where Kilkenny provided the opposition. A close game developed, however, a Martin Comerford goal secured the title for "the Cats" on a score line of 1-14 to 1-11.