Cian O'Connor (32) will compete alongside Billy Twomey for Ireland in show jumping.
O'Connor was brought in as a replacement for Denis Lynch, after the latter was withdrawn for competition at London 2012 by the OCI.
From Dublin, O'Connor represented Ireland at the Athens 2004 Olympics, when he won a gold medal, which was Ireland's only medal at the Games.
However, the medal was later stripped from him when his horse Waterford Crystal tested positive for a prohibited substance.
The FEI ruled that O'Connor be stripped of his medal and receive a three-month ban from competition.
His form in 2012 has included taking second place at both the Grand Prix - CSI3* in Wellington, Florida, and the FEI Nations Cup - CSIO4* also in Wellington, Florida.