Born in Banagher, County, Mannion first excelled at hurling in his youth. He first came to prominence on the inter-county scene when he first linked up with the minor team, before later joining the under-21 side. At club level Mannion is a one-time Leinster medallist with Saint
His retirement came during the 1997 championship.
In retirement from playing, Mannion became involved in team management and coaching. He served as a selector with the minor team for two seasons.
Saint Rynagh"s Leinster Senior Club Hurling Championship (1): 1993 Offaly Senior Club Hurling Championship (4): 1987, 1990, 1992 1993 Offaly Leinster Senior Hurling Championship (1): 1989, 1990 National Hurling League (1): 1990-1991 Leinster Under-21 Hurling Championship (1): 1989 All-Ireland Minor Hurling Championship (2): 1987, 1986 Leinster Minor Hurling Championship (2): 1986.
He made his senior debut during the 1988-1989 National League and immediately became a regular member of the team
