Alexander Downer's tip appears to have helped persuade the FBI to investigate Russian meddling in the US election and possible co-ordination with the Trump campaign, The New York Times reports.
Trump campaign adviser George Papadopoulos told the Australian High Commissioner to the UK, during a meeting in London in May 2016 that Russia had thousands of emails that would embarrass Democratic candidate Hillary Clinton, the report said.
Australia passed the information to the FBI after the Democratic emails were leaked, according to The Times, which cited four current and former US and foreign officials with direct knowledge of the Australians' role.
"The hacking and the revelation that a member of the Trump campaign may have had inside information about it were driving factors that led the FBI to open an investigation in July 2016," the newspaper said.
White House lawyer Ty Cobb declined to comment, saying in a statement that the administration is continuing to cooperate with the investigation now led by special counsel Robert Mueller "to help complete their inquiry expeditiously."
"Out of respect for the special counsel and his process, we are not commenting on matters such as this," he said in a statement.
Mueller has charged four Trump associates, including Papadopoulos, in his investigation.
Russia has denied interfering in the US election and Trump has said there was no collusion between his campaign and Moscow.
Papadopoulos has pleaded guilty to lying to the FBI and is a cooperating witness. Court documents unsealed two months ago show he met in April 2016 with Joseph Mifsud, a professor in London who told him about Russia's cache of emails.
This was before the Democratic National Committee became aware of the scope of the intrusion into its email systems by hackers later linked to the Russian government.
The Times said Papadopoulos shared this information with Downer, Australia's former foreign minister, but it was unclear whether he also shared it with anyone in the Trump campaign.
