The flight, which departed New York on Friday, is the first of three planned test flights involving the new Boeing 757-9s aircraft which are set to cover new direct routes between Sydney and, London and New York.
The flight with 49 people onboard took 19 hours and 16 minutes to reach Sydney on Sunday, a 16,200-km route, the BBC reported.
Passengers set their watches to Sydney time after boarding and were kept awake until night fell in eastern Australia to reduce their jetlag.
Six hours later, they were served a high-carbohydrate meal and the lights were dimmed to encourage them to sleep.
Onboard tests included monitoring pilot brain waves, melatonin levels and alertness as well as exercise classes for passengers and analysis of the impact of crossing so many time zones on people's bodies.
According to Qantas Group CEO Alan Joyce, the development was a "really significant first for aviation".
Competition in the ultra-long haul aviation market has intensified in recent years, with various airlines flying extended routes, the BBC reported.
Singapore Airlines launched a near-19 hour journey from Singapore to New York last year, which is currently the world's longest regular commercial flight.
Also last year, Qantas began a 17-hour non-stop service from Perth to London, while Qatar Airways operates a 17.5-hour service between Auckland and Doha.
( With inputs from IANS )