The court case started in the Federal Court six years ago, before a Full Court appeal, a trip to the High Court and finally back to Full Court of the Federal Court.
The penalty the Full Court meted out was higher than the original $11 million imposed by the trial judge in March 2014, which was appealed by both Flight Centre and the ACCC.
However, it was well short of the $17 million to $22 million range being sought by the regulator.
"The ACCC appealed from the initial $11 million penalty orders because it considered that this level of penalty was inadequate to achieve a strong deterrence message for Flight Centre and other businesses," ACCC Chairman Rod Sims said.
"Flight Centre is Australia's largest travel agency, with $2.6 billion in annual revenue," Mr Sims said.
"We will continue to argue for stronger penalties which we consider better reflect the size of the company, as well as the economic impact and seriousness of the conduct."