Giddy's first national competition was the National Games in 1969, and his first international competition was the 1970 Commonwealth Paraplegic Games in Edinburgh, where he won three gold medals and a silver medal. At the 1972 Heidelberg Paralympics, he won a silver medal in the Men's 100 m Wheelchair 4 event, and also participated in the Australia men's national wheelchair basketball team. He participated in the 1974 Commonwealth Paraplegic Games in Dunedin, New Zealand. He was selected but did not participate in the 1976 Toronto Paralympics due to illness, and also did not participate in the 1980 Arnhem Paralympics. He won a gold medal at the &lt;a href="1984%20Summer%20Paralympics"&gt;1984 New York/Stoke Mandeville Paralympics&lt;/a&gt; in the Men's Discus 4 event, a silver medal in the same event at the 1988 Seoul Paralympics, a silver medal in the Men's Discus THW6 event and a bronze medal in the Men's Shot Put THW6 event at the 1992 Barcelona Paralympics, and a bronze medal in the Men's Shot Put F55 event at the 1996 Atlanta Paralympics.