The former militia commander is the highest-level official to be sentenced by the International Criminal Court, or ICC, in what is being described as an historic case.
It is the first time the court has prosecuted sexual violence in warfare and command responsibility, where a superior is acccountable for actions by his subordinates.
"For the foregoing reasons, the chamber sentences Mr Jean-Pierre Bemba Gombo to a total of 18 years of imprisonment."
Jean-Pierre Bemba was in court to hear presiding judge Sylvia Steiner deliver the verdict.
In March, the ICC had found the former vice-president of the Democratic Republic of Congo guilty of five counts of war crimes and crimes against humanity.
They concerned atrocities in the neighbouring Central African Republic in 2002 and 2003 carried out by soldiers from a militia group he had created in the 1990s.
The court says, over a five-month period, around 1,500 men from the Congolese Liberation Movement were sent to the country to help quash a coup against the president.
The court says the soldiers raped, killed and looted with particular cruelty.
During the trial Chief Prosecutor Luis Moreno-Ocampo detailed some of what transpired.
"Small platoons were organised. Groups of three or four soldiers invaded houses one by one. They stole all the possessions that could be carried off and raped the women -- girls and elders, regardless of their age."
Delivering the court's heaviest sentence yet, Judge Steiner said Jean-Pierre Bemba was in a position to prevent the crimes from occurring but failed to do so.
"The chamber convicted Mr Bemba under Article 28(a) as a person that, effectively acting as a military commander, who knew that forces under his effective authority and control were committing or about to commit the crimes against humanity of murder and rape and the war crimes of murder, rape and pillaging, Mr Bemba did not genuinely intend to take all necessary and reasonable measures within his material ability to prevent or repress the commission of crimes."
The International Criminal Tribunal for the Former Yugoslavia in The Hague and its counterpart for Rwanda have both prosecuted rape as a war crime.
But there had never been a trial at the ICC focused on rape and sexual violence in the context of conflict.
London-based barrister Toby Cadman, a former chief prosecutor of the Bosnian war-crimes chamber, says it is one reason the Bemba case is so important.
He has told the BBC another reason is, for the first time, the court has prosecuted a senior commander over the crimes of his troops.
"It's the first case involving sexual violence and a commander being held responsible for the conduct of his soldiers. It is incredibly significant in that it's the first case by the ICC to prosecute rape as a weapon of war, something that a lot of people -- myself included -- have been pushing for for some time. There, obviously, has been some criticism about the length of time it's taken to come to trial and for the proceedings to be concluded. And, obviously, that is a concern -- between eight and 10 years. But because of the findings that the court has made, I think it is ... it will be regarded as a hugely significant step."
Toby Cadman says Bemba's MLC political party, born out of the militia group and now a major opposition force in the Democratic Republic of Congo, has condemned the sentence.
He says the trial result is likely to revive criticism that the court, established to prosecute the worst crimes under international law, is targeting Africans too heavily.
"We've seen it over the last couple of months through the African Union, through a number of African states, condemning the ICC for being a colonial, anti-African power. That's what we would expect to hear. We've also seen the situation with the Sudanese president (Omar) Al-Bashir when he was in South Africa and South Africa not properly cooperating with the ICC. So, there will be, of course, these concerns raised. And, of course, there have been a number of issues raised in terms of what the ICC is looking at when they should be looking at situations like Syria, Iraq and those conflicts."
The court says reparations for the victims will be considered at a future date and Bemba will receive credit for time spent in detention since his arrest in Belgium in 2008.
His defence team has already announced plans to appeal.
It is only the third sentence handed down by the court since it began operating in 2002.
All have been nationals of African countries.
