Walker competed in the Paralympics for the first time during the 2000 games, in Sydney. In all he took home three medals from these games, a bronze in the 100 m breaststroke SB7, silver in the 50 m freestyle S7 and gold in the 4×100 m freestyle 34 pts. As part of the gold medal winning relay team, which also included Jody Cundy, Giles Long and David Roberts, he set a new world record time of 4:06.85.