Jean-Pierre Bemba, who fled DR Congo last year, was detained in Belgium in May. He will face trial at the International Criminal Court (ICC).
Mr Bemba is accused over atrocities allegedly committed by his forces in the Central African Republic in 2002.
The one-time rebel leader has always denied the charges against him.
Mr Bemba went into exile after being accused of high treason in his home country for refusing to disarm his militia after his defeat in presidential elections in 2006.
"Jean-Pierre Bemba was a vice-president and is a senator," said ICC Prosecutor Luis Moreno-Ocampo.
"But he does not have immunity before the ICC, and will face justice."
The successful businessman was one of four vice-presidents in a transitional government in the war-torn African nation between 2003 and 2006.
He was leader of the rebel group, the Movement for the Liberation of Congo, which later became a political party.
In 2002, his group was asked by the former president of the Central African Republic, Ange-Felix Patasse, to help put down a coup attempt.
While there, Mr Bemba's forces were accused of widespread rights abuses.
After Mr Patasse was ousted the following year, his successor pressed charges against Mr Bemba of rape and murder.
The case was referred to the ICC in The Hague, which announced his arrest on 24 May.