Trump campaign adviser George Papadopoulos told the diplomat, Alexander Downer, during a meeting in London in May 2016 that Russia had thousands of emails that would embarrass Democratic candidate Hillary Clinton, the report said.
Downer, a former foreign minister, is Australia's top diplomat in Britain.
Australia passed the information on 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.
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."
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.