Cathal Moynihan competed for Ireland in the men's lightweight coxless four at the 2008 Beijing Olympic Games, competing at the Shunyi Olympic Rowing-Canoeing Park alongside Gearoid Towey, Richard Archibald and Paul Griffin.
From Killarney, Co. Kerry, Moynihan was a member of Muckross Rowing Club, based on the shores of Lough Leane - one of six rowing clubs in the town that has produced a remarkable tradition of international oarsmen. Three Killarney rowers competed at those Games - Moynihan and Paul Griffin in the lightweight four, and Sean Casey in the heavyweight four.