McDonnell first came to prominence on the inter-county scene as a member of the Cork minor hurling and football teams in 1968. He made his hurling debut in the provincial decider on 21 July 1968 and collected a Munster medal following a 7–8 to 5–4 defeat of Waterford. McDonnell was an unused substitute for Cork's subsequent All-Ireland final defeat by Wexford. Also that year he claimed a Munster medal with Cork's footballers following a 4–15 to 4–10 defeat of Clare. He was dropped from the starting fifteen for Cork's subsequent 3–5 to 1–10 All-Ireland final defeat of Sligo.