Prime Minister Scott Morrison said the country had struck two deals that would allow free doses to be rolled out in 2021 if they were approved for use.
Mr Morrison estimated the cost to be A$1.7bn (£0.9bn; $1.24bn).
Australia's 25 million people could begin receiving doses from January but there were "no guarantees", he said.
"However the agreement puts Australia at the top of the queue, if our medical experts give the vaccines the green light," the prime minister said.