Tadhg competed as part of the South African Paralympic swimming team at six Paralympic games. His first games in 1992 gave him his first Paralympic gold medal in the 100m breaststroke in a world record time as well as finishing fourth in his heat in the 50m freestyle, eighth in the final of the 50m butterfly, seventh in his heat of both the 100m and 400m freestyle. In the 1996 Summer Paralympics he finished second in the 100m breaststroke behind Kasper Engel of the Netherlands who set a new world record, he also competed in the 50m freestyle finishing 28th in the heats, 50m butterfly where he finished ninth in the heats just missing the final and finished fourth in the final of the 200m medley. At his third games in 2000 he again won silver in the 100m breaststroke behind Kasper and added a second in the 200m medley behind the new world record set by Sascha Kindred of Great Britain, as well as finishing seventh in the 50m butterfly. Tadhg won gold again in 2004 Summer Paralympics in the 100m breaststroke, beating his old rival Kasper Engel he also competed in the 200m medley finishing sixth but could not make the final of the 50m butterfly. His fifth games in 2008 led to his first bronze medal, in his favoured 100m breaststroke and finished last in his heat in the 200m individual Medley. And his final sixth games in 2012 led to his fifth place. He is now retired from international swimming. He is now a full-time swimming coach for the disabled in Johannesburg, South Africa.