Following the war, Serong returned to Melbourne but struggled to return to civilian life and lived apart from his family, who had begun to live their own lives in his long absence. He was considered a world authority on counter-insurgency operations, and wrote widely on the subject in the 1970s. Described by John Farquharson as a major Cold War figure, Serong was recognised internationally for developing new tactics for counter-insurgency and jungle warfare. In retirement he became involved in anti-communist organisations and citizens' militia groups such as Ausi Freedom Scouts (Australians United for Survival and Freedom), of which he was a patron. He also supported conspiracy theories about the Port Arthur shooting in 1996 and allegations of government corruption (later found to have been based on a hoax, albeit unbeknown to Serong) as well as speaking on Australian defence issues. He was at times associated with right-wing individuals or organisations, advocating nationalism and the need for increased defence spending as part of a "forward defence" strategy, as well as strengthening of the peace-time Army Reserve, the development of inland Australia, opposition to gun control, concerns about the loss of national sovereignty and financial autonomy to the United Nations and International Monetary Fund, and limitations on immigration. While at times a controversial figure, his public reputation remained high and his opinions were rarely the subject of criticism in the media. Serong died of heart disease on 1 October 2002 and was survived by his wife and their three daughters and three sons. He was aged 86.