Brendan McCarthy competed in the men’s flyweight boxing at the 1968 Mexico City Olympic Games, losing his opening bout on a unanimous points decision to Ricardo Delgado of Mexico – the eventual gold medallist. A member of the Arbour Hill Boxing Club, McCarthy was one of three Arbour Hill representatives on the Irish boxing team at those Games, alongside Mick Dowling and Eddie Tracey.

His opponent Delgado went on to win the flyweight gold medal, reflecting the quality of the competition McCarthy faced in his Olympic debut.