Judge John Gillen ruled the evidence in the civil case against Colm Murphy and Seamus Daly was overwhelming, the BBC reported.
"The barrier of time has not served to disguise the enormity of this crime, the wickedness of its perpetrators and the grief of those who must bear its consequences," the judge said.
"Even 15 years on nothing can dilute the pulsing horror of what happened."
No one has ever been convicted on criminal charges in the bombing.
The families of those killed in the Real IRA attack in the Tyrone County city of about 51,000 have been awarded $2.4 million. An attorney for the families said efforts to collect the damage award would be "pursued with vigor," the British network said.
Michael Gallagher, whose son Aidan died in the bombing, called the outcome of the second trial, which came after the pair of defendants successfully appealed the verdict in their first trial four years ago, an "important judgment."
"We will be pursuing the judgment because it would be a very hollow judgment if it was merely words," he said.
"We will be doing our best to try and recover the damages but at the moment, we're just happy that we've got a judgment that we, the families, the victims, have held someone to account for what happened at Omagh."