Judges may made a decision to impose a life sentence instead, but in their ruling the judges said because numerous individual crimes involve overlapping conduct, they did not warrant a life sentence.
He said the court had taken the "particular cruelty" of some of Ntaganda's crimes into account. The judge highlighted several specific crimes committed by Ntaganda and his men, including the brutal rape of a 13-year-old girl and the murder by the rebel leader himself of a Catholic priest.
Ntaganda stood motionless in the high-security courtroom as he listened through headphones while the judgement was read out. The long list of offenses, committed in the Democratic Republic of the Congo in 2002 and 2003, included murder, rape, sexual slavery, enlisting child soldiers, persecution, forcible transfer and deportation, pillage and intentionally directing attacks against civilians.
Ntaganda, born in Kinigi in Rwanda, had his first taste of combat in Uganda, where he joined the Rwandan Patriotic Front (RPF) in 1990 at the age of 17 and fought alongside Paul Kagame to overthrow Rwanda's genocidal regime in 1994.
He told the defendant there were no real mitigating circumstance in his case, but said his crimes, "despite their gravity and his degree of culpability", did not merit a life sentence.
The ICC is an global court set up in 2002 to prosecute war crimes and crimes against humanity when member states are unable or unwilling to do so.
The court heard fearful villagers dubbed him "Terminator" after the Arnold Schwarzenegger film about a merciless robotic killer.
ICC judges found Ntaganda guilty of 18 counts in July, including murder, rape, sexual slavery and enlisting child soldiers.
The first-ever suspect to voluntarily surrender to the ICC, Ntaganda walked into the United States embassy in the Rwandan capital Kigali in 2013 and asked to be sent to the court in the Netherlands.
He surrendered to the US Embassy in Rwanda in 2013 and his trial began two years later, with closing arguments presented in August 2018.
Ntaganda's UPC, dominated by the Hema clan, violently attempted to expel the Lendu people from DRC Congo's mineral-rich Ituri region in the country's far north-east.
The ICC had issued its first arrest warrant against Ntaganda for war crimes in Ituri in 2006 and the warlord became a symbol of impunity in the region.
Ntaganda's boss, UPC leader Thomas Lubanga, is serving a 14-year prison sentence after his conviction at the ICC on charges of conscripting and using child soldiers.
The ICC has suffered a string of setbacks over recent years with some of its most high-profile suspects walking free, including Ivorian former leader Laurent Gbagbo earlier this year. The court has also been criticised for mainly trying African suspects.