Sillitoe competed for the Coburg Athletic Club. Upon his retirement, he took up athletics coaching and helped lay the foundations for one of the most successful eras of Australian sprinting with the East Melbourne Harriers Athletic Club. Australian representatives that Sillitoe has coached include Peter Norman, Gary Holdsworth, Greg Lewis, Aaron Rouge-Serret, Colin McQueen, Denise Boyd, Richard James, Bruce Frayne, Tamsyn Lewis and Ken Hall. He was the coach of the 1982 Commonwealth Games Team and held a long serving athletics coaching post with Caulfield Grammar School in Melbourne from 1983 to 2014.