Bosco Ntaganda was found guilty of 13 counts of war crimes and five counts of crimes against humanity in July. 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.
Nicole Samson, one of the court's prosecution lawyers, told CNN the magnitude of the crimes in the case was "extreme."
She added she believed the judgment and the fact that Ntaganda has been found responsible was important for his victims.
"It's the first time for them that they will have any sense of justice for the crimes that were committed against them and their communities."
The sentence is the longest handed down by the ICC and he also becomes the first person to be convicted of sexual slavery.
In a statement, the ICC said the sentencing was unanimous. The time Ntaganda had already spent in detention, from March 22, 2013, to November 7, 2019, would be deducted from his sentence, the Hague-based court said.
Samson said that the high sentence "should give other potential perpetrators cause to pause and consider that they will be immune from justice should they continue."
The defense and prosecution has 30 days to appeal.
The ICC issued an arrest warrant for Ntaganda -- who fought for various rebel groups before becoming a general in the Congolese army -- in 2006.
He surrendered to the US Embassy in Rwanda in 2013 and his trial began two years later, with closing arguments presented in August 2018.