The Wexford-born back row has scored six tries in 37 appearances in all competitions for the region.
Phil Davies, Director of Rugby, said: "We are clearly disappointed that Robin will leave at the end of his contract. But when we do reach the end of the season he will go with our best wishes and thanks for all he has given to the Blues shirt.
"Robin joined us as a Championship player, after his spell at Rotherham, and will leave us a potential international. We are immensely proud of the hard work, both on his part and that of the region, to develop him as a player.
"I have always known that he had a huge desire to play for Ireland and this is a major factor behind this move.
"Robin has always given his absolute all for the Blues and I know he will continue to lead from the front in his last season with us."
Richard Holland, Chief Executive at Blues, added: "Robin has made a big contribution, both on and off the field, during his time here and we have done everything in our power as a region to try and extend his stay at the Arms Park.
"However, Robin has stated his aspiration to play for his country and he has taken a decision on what he feels is the best route for him to achieve that.
"We now look forward to him continuing to give everything for Blues this season in all competitions as we strive to reach the knock out stages of the Heineken Cup in the coming months and climb the RaboDirect PRO12 table."