Visiting Australia for the first time as leader, Mark Carney told the Lowy Institute in Sydney that coalitions with like-minded allies were needed more than ever after US and Israeli strikes on Iran were met with retaliatory attacks.
Mr Carney described Iran as a "serial offender of international law" and "principal source of instability and terrorism".
He lambasted its targeting of several Gulf states in the region.
But he also diverted from his initial steadfast support of American and Israeli actions killing Ayatollah Ali Khameini, saying they needed to respect the rules of engagement.
"We take this position with some regret, because the current conflict is another example of the failure of the international order," he told a packed audience on Wednesday evening.
He said Canada was prepared to assist in bringing an end to hostilities in the Middle East.
Canada and Australia had legitimacy and trust on their side and other countries looked to them for stability, he said.
Both nations had the capacity to rebuild a global order based on the values of respect for human rights, sovereignty and territorial integrity.
"Australia and Canada can't compel like the great powers, but we can ... set the agenda," he said.
In a pointed criticism of military campaigns, Mr Carney noted "change through compulsion doesn't last."
He said unlike global superpowers "acting without constraint or respect for international norms or laws", nimble middle-power coalitions had a tactical advantage.
"We can ... shape the rules, and organise and build capacity through coalitions that deliver results at speed and global scale," Mr Carney said.
"Middle powers have more power than many realise."
Mr Carney touched on aspects of his blistering speech at the World Economic Forum in Davos, Switzerland that gained global attention, referring to the memorable line "if we're not at the table, we're on the menu".
Earlier on Wednesday, he took steps to ensuring both Australia and Canada's super-sized pension funds would co-operate more closely to compete on the global economic stage.
Nine Australian funds, representing 14 million accounts and $1.4 trillion in assets, inked an agreement with Canadian funds that would help get them get more bang for their investment buck.
The countries' respective pension systems are forecast to manage a combined $20 trillion in assets by 2040.
As of 2024, Canadian direct investment into Australia was about $60 billion, while about $30 billion was headed in the other direction, the Canadian government said.
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