|Competitor for Australia|
|Gold||2000 Sydney||4×200 m freestyle|
|World Championships (LC)|
|Gold||2001 Fukuoka||4×200 m freestyle|
|World Championships (SC)|
|Gold||1997 Gothenburg||4×200 m freestyle|
|Pan Pacific Championships|
|Gold||1999 Sydney||4×200 m freestyle|
|Silver||1998 Kuala Lumpur||200 m Butterfly|
William ("Bill") Ashley Kirby (born 12 September 1975 in Perth, Western Australia) is an Australian swimmer who was competitive on an international level in the nineties and early 2000s. He specialized in freestyle and butterfly and won a gold medal at the 2000 Summer Olympics in Sydney as part of the 4×200m freestyle relay team. He was an Australian Institute of Sport scholarship holder.
Kirby made his debut at the 1993 Pan Pacific Championships before competing at the 1994 Commonwealth Games in Victoria, Canada and the 1994 World Aquatics Championships in Rome as a butterfly swimmer. After missing selection for the 1996 Summer Olympics in Atlanta, due to glandular fever, he contemplated quitting the sport.
Kirby found his way back into the national team at the 1997 FINA World Short Course Swimming Championships in Gothenburg, Sweden. Although he missed selection for the 1998 World Aquatics Championships in his home town, he bounced back to qualify for the 1998 Commonwealth Games in Kuala Lumpur, where he won a silver medal in the 200m butterfly. At the 1999 Pan Pacific Championships in Sydney, he was a member of the 4×200m freestyle relay team (along with Michael Klim, Ian Thorpe and Grant Hackett) that lowered the world record, at the time, to 7m 8.79s. Training at the Australian Institute of Sport, he earned an Olympic berth the following year, anchoring the Australian 4×200m relay team of Thorpe, Klim and Todd Pearson to another world record of 7m 7.05s.
Kirby's final international competition was at the 2001 World Aquatics Championships in Fukuoka, Japan, where along with Klim, Hackett and Thorpe, he lowered the 4×200m freestyle relay world record to 7m 4.66s. That record held firm for nearly six years until United States relay team clocked in at 7m 3.24s at the 2007 World Championships in Melbourne, Australia.
Kirby also collected a gold for swimming in the non-final heats of the 4×100m freestyle relay and also swam in the finals of the 200m freestyle individual event. He retired after the championships to start a coaching career and business.
He now teaches swimming at Christ Church Grammar School, the school at which he was educated.