Ciara Sheehy competed in the women's 4x400 metres relay at the 2000 Sydney Olympic Games alongside Karen Shinkins, Emily Maher and Martina McCarthy, the team setting a new Irish national record of 3:32.24 in their heat.
A powerful first leg from Shinkins placed the team second at the end of the opening lap before they finished third in the heat. It was a relay campaign notable for its strong collective preparation: the squad arrived in Sydney early, marching at the Opening Ceremony and allowing two weeks to acclimatise before their event, a strategy that contributed directly to the national record performance.