Unlike many of his hurling colleagues, Simpson didn’t make the county panel at minor or under-21 levels. Most of his leisure time was taken up playing soccer. As a centre half or sweeper with his local club, East End, he won every honour possible in the Kilkenny and District League. In the late 1980s Simpson joined the Kilkenny junior hurling team and won Leinster and All-Ireland honours at this level in 1990. His performances for the team brought him to the attention of the senior selectors and he made his debut in 1991. That year Simpson won his first Leinster title, however, Kilkenny later lost the All-Ireland final to Tipperary. ‘The Cats’ continued their provincial dominance in 1992 with Simpson collected a second Leinster medal. Kilkenny subsequently defeated Cork in the championship decider, giving Simpson his first All-Ireland medal. His performance throughout the championship also earned him his first All-Star award.
The following year Simpson won a third consecutive provincial title and Kilkenny later qualified for a third consecutive All-Ireland final appearance. Galway provided the opposition on that occasion, however, Kilkenny powered to another victory and Simpson won a second All-Ireland medal. He later picked up a second All-Star award. Kilkenny lost their provincial crown in 1994, however, Simpson won a National Hurling League medal in 1995. He retired from inter-county hurling shortly afterwards.