College During his schooling at
Presentation Brothers College McDonnell played with various
rugby union teams. He won back-to-back
Munster Junior Cup medals in 1965 and 1966 following respective defeats of
Rockwell College and
St. Munchin's College. McDonnell also played for the Munster Schoolboys Senior Team in the 1968 Interprovincial series.
University During his studies at
University College Cork McDonnell came played competitively as a hurler and as a rugby player. On the rugby field, McDonnell won a Nunan Cup medal in 1969–70. He also played on a number of other teams in UCC including the junior and senior teams. McDonnell was as a member of the university's senior hurling team, and played at full-back on the UCC team that faced rivals
University College Dublin in the
Fitzgibbon Cup decider in 1969. A narrow 1–12 to 1–10 defeat was the result on that occasion. Two years later McDonnell was captain of the UCC team that faced
University College Galway in that year's decider. A 2–16 to 2–6 victory gave McDonnell a Fitzgibbon Cup medal. McDonnell was at full-back on the team for the last time in 1972 as University College Cork reached a third decider in four seasons. A 3–11 to 0–6 beating of University College Galway gave McDonnell his second successive Fitzgibbon Cup medal.
Club McDonnell began his club hurling career at under-14 level with
Aghabullogue in 1962. He later moved to
Inniscarra where he joined their under-14 team in 1964. As a student McDonnell had success on the club scene as a member of the University College Cork team in 1970. After losing seven finals in the previous thirteen years (including a replay), the collegians finally won a championship medal through a 2–12 to 0–16 defeat of
Muskerry which, ironically, was McDonnell's home division. It was his first
championship medal. In 1975 Inniscarra reached the junior championship decider after winning the divisional crown. McDonnell was at full-back as
Ballymartle provided the opposition. After leading by 2–2 to 1–2 at half-time, Inniscarra went on to score a further three goals after the interval. A 5–7 to 3–8 victory gave McDonnell a
championship medal in the junior grade.
Minor, under-21 and intermediate 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. In 1969 McDonnell made his under-21 debut in an 8–14 to 1–1 Munster semi-final defeat of
Galway. He missed the subsequent provincial final victory but was introduced as a substitute in the All-Ireland final against Wexford on 14 September 1969. A 5–13 to 4–7 victory gave McDonnell his first
All-Ireland medal. That same year McDonnell was drafted onto the Cork intermediate team. He won a
Munster medal following a 4–14 to 0–6 win over Galway before later lining out against
Kildare in the All-Ireland decider on 12 October 1969. A 2–8 to 3–4 defeat was the result on that occasion. McDonnell won his first
Munster medal with the under-21s in 1970 following a 3–11 to 2–7 defeat of
Tipperary. Cork faced Wexford in the subsequent All-Ireland decider on 11 October 1970, however, that game ended in a 3–8 to 2–11 draw. The replay three weeks later was more conclusive, with Cork winning with a 5–17 to 0–8 victory. It was McDonnell's second All-Ireland medal. In 1971 McDonnell was named captain of the under-21 team. He won a second Munster medal that year following a 5–11 to 4–9 defeat of Tipperary. On 12 September 1971 Wexford stood in the way of Cork securing a record-breaking fourth successive championship and a high-scoring game ensued. A 7–8 to 1–11 victory gave McDonnell his third successive All-Ireland medal, while he also had the honour of lifting the cup.
Senior Early successes McDonnell made his senior debut for Cork during their 1969–70 National League campaign. It was a successful campaign for the Rebels as an aggregate 5–21 to 6–16 defeat of
New York gave McDonnell his first
National Hurling League medal. The subsequent championship campaign saw McDonnell win his first
Munster medal as Tipperary were beaten 3–10 to 3–8. Cork subsequently faced Wexford in the All-Ireland decider on 6 September 1970. A record 64-point scoreline and eleven goals were produced in the contest. The day belonged to
Eddie O'Brien who scored a hat-trick of goals for Cork from his hand as Cork secured a 6–21 to 5–10 victory. It was McDonnell's first
All-Ireland medal. He finished the year by becoming the youngest recipient of the
Texaco Hurler of the Year award. After a less successful season under McDonnell's captaincy in 1971, McDonnell had more success in 1972 when he won a third league medal following a 3–14 to 2–14 defeat of
Limerick. He later added a second Munster medal to his collection following a 6–18 to 2–8 win over
Clare. Rivals
Kilkenny provided the opposition in the subsequent All-Ireland final on 3 September 1972. Halfway through the second-half Cork were on form and stretched their lead to eight points. Kilkenny's
Eddie Keher was deployed closer to goal and finished the game with 2–9. A fifteen-point swing resulted in Kilkenny winning the game by 3–24 to 5–11. McDonnell was dropped from the Cork panel in 1973, however, he returned in 1975 and collected a third Munster medal following a 3–14 to 0–12 defeat of reigning provincial champions Limerick.
Three-in-a-row "The Rebels" retained the provincial title in 1976 following a 3–15 to 4–5 defeat of Limerick once again. It was McDonnell's fourth winners' medal. Wexford provided the opposition in the subsequent All-Ireland final on 5 September 1976. Wexford got off to a great start and were 2–2 to no score ahead after just six minutes. Wexford had a two-point lead with ten minutes to go, however, three points from
Jimmy Barry-Murphy, two from
Pat Moylan and a kicked effort from
Ray Cummins gave Cork a 2–21 to 4–11 victory. It was McDonnell's second All-Ireland medal. Cork faced Clare in the provincial decider in 1977, on a day when armed robbers made away with the takings from the gate of £24,579 during the second half of the game. Clare conceded an early penalty but they fought back to take the lead until a red card for full back
Jim Power turned the tide for Cork and they eventually won by 4–15 to 4–10, with McDonnell collecting a fifth winners' medal. He was dropped from the starting fifteen for Cork's subsequent All-Ireland campaign, however, he did collect a third All-Ireland medal as a non-playing substitute following Cork's 1–17 to 3–8 defeat of Wexford. McDonnell lost his place on Cork's championship fifteen in 1978. In spite of this he collected another Munster medal as a non-playing substitute following Cork's 0–13 to 0–11 provincial final defeat of Clare. McDonnell was listed amongst the substitute for Cork's subsequent All-Ireland game against Kilkenny on 3 September 1978. A 1–15 to 2–8 victory secured a third championship title in succession and a fourth All-Ireland winners' medal for McDonnell, his second as a substitute. Injuries had led to McDonnell playing a reduced role in the previous few years and he retired from inter-county hurling following Cork's three-in-a-row success.
Inter-provincial McDonnell also was selected for
Munster in the inter-provincial series of games. He won his sole
Railway Cup medal as an unused substitute in 1976, when Munster defeated
Leinster by 4–9 to 4–8. ==Post-playing career==