Born in Aghabullogue, County Cork, attended secondary school at Presentation Brothers College, Cork. He arrived on the inter-county scene at the age of eighteen when he first linked up with the Cork minor team before later joining the under-21 and intermediate sides. He made his senior debut during the 1969–70. McDonnell immediately became a regular member of the starting fifteen and won two All-Ireland medals, five Munster medals and two National Hurling League medals. He was an All-Ireland runner-up on one occasion.