Bemba appeared before the ICC in The Hague in January for a hearing to confirm the charges against him, following his arrest on an ICC warrant during a visit to Brussels in May 2008.
After a years-long civil war in the DRC, Bemba became one of four vice-presidents in a transitional government ahead of elections in the country in 2006.
He unsuccessfully challenged Joseph Kabila for the presidency.
Bemba then led the opposition, but was forced into exile when government forces tried to disarm his private militia in clashes that killed at least 300 people in March 2007.
Prosecutors claim Bemba had sent 1,000 to 1,500 troops to the CAR to retain control of the border area with the Congolese province of Equateur in a war between his Movement for the Liberation of Congo (MLC) and the then DRC leader Laurent Kabila, the father of the current president.
While there, the prosecution alleges that MLC militia brutally gang-raped men, women and children, and tortured and murdered civilians.
Bemba had argued before the court in January that MLC militia in the CAR had not been under his command when deployed to help put down a coup.
His lawyers told the court that the men were under the command of Ange Felix Patasse, the then CAR president, whose government provided their transport, fuel, money and uniforms, while Libya supplied the weapons and ammunition.
They claimed the case was part of a conspiracy to sideline Bemba politically.
But in their decision on Monday, the pre-trial judges said there was evidence that Bemba "actually knew about the occurrence of the crimes".