Gough Whitlam, Australian Labor Party prime minister in the early 1970s, made his comment after Singapore turned down repeated pleas for clemency for 25-year-old Nguyen Tuong Van.
Van Nguyen is scheduled to go to the gallows on 2 December after being convicted of trafficking 400g of heroin in 2002.
Whitlam urged Prime Minister John Howard to use the Commonwealth Heads of Government Meeting (CHOGM) in Malta to plead again for Van Nguyen's life.
"If CHOGM is of any use then it should be raised there, because it concerns many other countries - some larger, some smaller than the rogue Chinese port city," he told Melbourne broadsheet The Age on Friday.
Howard has said he will not attempt to marshal international support in Malta for his clemency pleas, saying the move would likely harden Singapore's resolve to execute Van Nguyen.
Another former prime minister, Bob Hawke, who strengthened Australia's ties with Asia during his time in office, also said he sent a letter to Prime Minister Lee Hsien Loong appealing for clemency. Hawke declined to detail the letter's contents.
Downer: It will be futile to take
Van Nguyen's case to the UN
Lex Lasry, a lawyer for Van Nguyen, thanked the former leaders for their support, but said Whitlam should have reined in his anger.
"I am pleased that my client has their support and I am pleased they have taken an interest," Lasry said. "But pejorative language probably will not help. No doubt Mr Whitlam feels frustrated by the case, as we all do."
Hoping for miracles
Foreign Minister Alexander Downer said on Friday an international law expert had told Canberra that it would be futile to take Van Nguyen's case to the UN's International Court of Justice.
"We just have to keep pleading to Singapore to reconsider and understand the strength of feeling here in Australia and hope that by some miracle they would decide to change their minds," he said.
"There's always a miracle," Downer added, "but I can't imagine what it is."
A senior lawmaker from Van Nguyen's home state, Victoria, visited Singapore's senior minister of state for law and home affairs on Thursday in a last-ditch appeal for mercy, but came away empty handed and critical of the city-state's punishment regime.
"There's always a miracle, but I can't imagine what it is"
Australian Foreign Minister
"This is a modern country, there's no doubt about that. But it seems to me that the punishments that it's meting out, whether the death penalty or caning people, don't belong to a 21st century justice system," Victoria state Attorney-General Rob Hulls said after the meeting.
A statement issued by Singapore's Law Ministry appeared to slam the door on any hope it will allow Van Nguyen to live.
"Nguyen had committed a very serious offence under our laws," the statement said.
"Singapore had a multi-pronged approach to combating the scourge of drug addiction and one component of our approach was the mandatory death penalty for drug traffickers, who were in fact the source of the drugs that ruined the lives of addicts."
"The law must now take its course," the statement said.