The Boeing 787-9 with 49 people on board took 19 hours and 16 minutes to fly from New York to Sydney, a 16,200-km (10,066-mile) route.
Next month, the company plans to test a non-stop flight from London to Sydney.
Qantas expects to decide on whether to start the routes by the end of 2019.
If it goes ahead with them, the services would start operating in 2022 or 2023.
No commercial aircraft yet has the range to fly such an ultra-long haul route with a full passenger and cargo load, Reuters news agency reports.