At Sydney 2000, William Kirby joined with Ian Thorpe, Michael Klim and Todd Pearson to shatter the world record when winning the gold medal in the 4 x 200 metres relay. The same four swimmers had set the world record at the 1999 World Championships. A year after the Sydney 2000 triumph Kirby, Klim, Thorpe and Grant Hackett won the same event at the 2001 World Championships.
Perth born Kirby moved to the AIS in Canberra to focus on swimming after completing his degree. He was an accomplished butterfly swimmer who missed the Atlanta 1996 Olympics due to glandular fever. He stuck with the sport and all the hard work paid off when he was in peak condition to anchor the relay team to gold at the Olympic Games in Australia.
After finishing his career as a competitor he establish swimming schools back in Perth.