"The chamber sentences Mr Jean-Pierre Bemba Gombo to a total of 18 years of imprisonment," said judge Sylvia Steiner, passing the tribunal's toughest term to date.
In justifying the stiff ruling, she said the former militia leader had failed to exercise control over his private army sent into CAR in late October 2002 where they carried out a series of "sadistic" rapes, murders and pillaging of "particular cruelty."
The atrocities were carried out by Bemba's private army, the Congolese Liberation Movement (MLC), when he sent them into neighbouring CAR in late October 2002 to put down a coup against then president Ange-Felix Patasse.
The 1,500 troops unleashed a five-month campaign of terror, during which the judges said "entire families were victimised" and which was aimed at squashing any resistance to Patasse's rule.
The case however is likely to drag on for a few more years, as his defence team has already filed notice that it intends to appeal the conviction, and argued that Bemba should be released immediately as he has been behind bars since his arrest in 2008.
But the three-judge bench said it had "not found any mitigating circumstances" to allow a reduction in sentence.
Reading out their findings at the world's only permanent war crimes court, based in The Hague, judge Steiner said Bemba had done "more than tolerate the crimes as a commander".
Bemba, a rich businessman who became one of the vice presidents of the Democratic Republic of Congo, was arrested in Brussels in 2008 after losing a bid for his country's presidency.
His case was the first at the ICC to focus on rape as a weapon of war and the first to highlight a military commander's responsibility for the conduct of the troops under his control.
