The man, who has remained anonymous, bought the ticket in January last year.
After finding the docket in a shopping bag this month, he checked his numbers online and realised he had won a A$1,020,496 (£630,000; $780,000) prize.
"I'm glad I didn't just get the old bags and take them to the dump," he said in a statement.
The winner, from the New South Wales (NSW) city of Newcastle, said he had been "a bit stupid" by forgetting about his ticket for 414 days.
"I'm not worried that I could have had the money a year ago. At least I've got it now," he said.
