Bosco Ntaganda faces a maximum life sentence after being convicted of war crimes and crimes against humanity.
The International Criminal Court judges convicted Congolese rebel warlord Bosco "Terminator" Ntaganda of war crimes, including directing gruesome massacres of civilians, rape and sexual slavery.
Finding him guilty of war crimes and crimes against humanity after a three-year trial in The Hague, head judge Robert Fremr said Ntaganda was a "key leader" who gave orders to "target and kill civilians" in Democratic Republic of Congo's Ituri region in 2002 and 2003.
Prosecutors gave horrific details of victims including some who were disembowelled and had their throats slit, as part of the evidence during his three-year trial in The Hague.
The soft-spoken Ntaganda -- known for his pencil moustache and a penchant for fine dining -- told judges during his trial that he was "soldier not a criminal" and that the "Terminator" nickname did not apply to him.
Rwandan-born Ntaganda faces 13 counts of war crimes and five counts of crimes against humanity for his role in the brutal conflict that wracked the northeastern region.
Prosecutors portrayed him as the ruthless leader of ethnic Tutsi revolts amid the wars that wracked the Democratic Republic of Congo after the 1994 genocide of Tutsis in neighbouring Rwanda.
More than 60,000 people have been killed since the violence erupted in the region in 1999 according to rights groups, as militias battle each other for control of scarce mineral resources.
High profile setbacks
Prosecutors said Ntaganda was central to the planning and operations for the Union of Congolese Patriots rebels and its military wing, the Patriotic Forces for the Liberation of Congo (FPLC).
The FPLC killed at least 800 people as it fought rival militias in Ituri, prosecutors said.
Formerly a Congolese army general, Ntaganda then became a founding member of the M23 rebel group, which was eventually defeated by Congolese government forces in 2013.
The first-ever suspect to voluntarily surrender to the ICC, he walked into the US embassy in the Rwandan capital Kigali in 2013 and asked to be sent to the court, based in the Netherlands.
Ntaganda is one of five Congolese warlords brought before the ICC, which was set up in 2002 as an independent international body to prosecute those accused of the world's worst crimes.
Ntaganda's former FPLC commander Thomas Lubanga was sentenced to 14 years in jail in 2012.
But it has suffered several setbacks over recent years with some of its most high-profile suspects walking free, while it has also been criticised for mainly trying African suspects so far.
In a separate hearing on Monday, judges are to determine whether there is enough evidence for a Malian jihadist to face trial for demolishing Timbuktu's fabled shrines, as well as for rape, torture and sex slavery.
Al Hassan Ag Abdoul Aziz Ag Mohamed Ag Mahmoud was captured and transferred to the court last year.