William Walker (born 31 October 1985 in Subiaco, Western Australia) is a retired Australian professional road racing cyclist and Australian Champion who rode for the Dutch team Rabobank between 2005 and 2008 and Spanish team Fuji–Servetto in 2009. Walker was described as having a motor on par with Lance Armstrong, with a reported recorded VO₂ max 94. Walker was also heralded as Australia's next Cadel Evans.

Walker finished second to Dmytro Grabovskyy in the Under 23 World Road Championship in Madrid in 2005. In 2006 he famously crossed the line first in the 2006 Australian Road championships and was awarded the gold medal in both the Elite and Under 23 categories, being the first Under 23 rider in history to race in the Australian champion jersey.

Walker represented Australia in the 2003, 2005, 2007 and 2008 World Road Championships as well as the 2006 Commonwealth Games in Melbourne. He also raced for Rabobank in the 2006 Vuelta España and the 2007 Giro d'Italia.

Walker did not ride for Fuji-Servetto in 2010 due to health issues. He returned to racing in 2012, making a successful return winning the 2012 Tour of Gippsland for Drapac Pro Cycling. Walker moved to the Azerbaijan-based Synergy Baku Cycling Project for the 2014 season. Walker was riding in the Australian National Road Race Championships in January 2014 when he suffered from sustained ventricular tachycardia and he retired from the race and from professional cycling.