The airline's "Project Sunrise" service, which has been repeatedly delayed, will cut up to four hours off the flight time between the two cities, the airline said in a statement.
"Qantas was built on the belief that Australia's distance from the rest of the world should never stand in the way," chief executive Vanessa Hudson said.
"The pioneering spirit of generations of our people has forged that path ever since, and today is the most significant step in that mission in our 105-year history."
Qantas said it would fly passengers non-stop on the Sydney-London route aboard its new ultra-long-range Airbus A350-1000ULR, which has undergone test flights in Toulouse, France.
The Airbus aircraft, which has been designed specifically for the across-the-world flight, carries an extra 20,000-liter rear center fuel tank to enable non-stop commercial flights of up to 22 hours.
