Robert McDonnell was a travelling reserve for Ireland’s mixed 4×400 metres relay squad at the Tokyo 2020 Olympic Games, where the team reached the final and finished 6th.

He was named in the relay pool of six athletes alongside Cillin Greene, Chris O’Donnell, Phil Healy, Sophie Becker and Cliodhna Manning, but did not run in either the semi-final or final.

At 19 years old, he was the youngest member of the entire Irish athletics team at the Games. From Galway, McDonnell is a member of Galway City Harriers and was coached by Brendan Glynn. In the build-up to Tokyo he won the Irish Under-20 200 metres title and took bronze in the senior national 400 metres championships, with a personal best of 46.59 seconds set at the Mary Peters Track in Belfast in May 2021.