Most of the charges against Rwandan-born Ntaganda, 46, related to a series of gruesome massacres of villagers carried out by his fighters.
"Murder was committed on a large scale," presiding judge Robert Flemr said, adding that the Hague-based court had taken the "particular cruelty" of some of Ntaganda's actions into account. "The overall sentence imposed on you shall therefore be 30 years of imprisonment."
But while the judges gave him the maximum sentence allowed by the ICC in terms of the number of years, they said that "despite their gravity" his crimes did not warrant a full-life prison term. Ntaganda, dressed in a blue suit and shirt and wearing a red tie, showed no emotion as the sentence was passed in the high-security courtroom.
An ICC spokesman confirmed it was the heaviest ever sentence handed down to date by the court, which was set up in 2002 to try the world's worst crimes. Ntaganda has appealed against his conviction earlier this year on 13 counts of war crimes and five of crimes against humanity - which saw him become the first to be convicted by the ICC of sexual enslavement.
Human Rights Watch welcomed the prison term.
"Bosco Ntaganda's 30-year sentence sends a strong message that even people considered untouchable may one day be held to account," said Ida Sawyer, deputy director of Human Rights Watch's Africa division. "While his victims' pain cannot be erased, they can take some comfort in seeing justice prevail."
A refugee from the 1994 genocide of Tutsis in Rwanda, Ntaganda emerged as a ruthless driver of ethnic Tutsi revolts that subsequently convulsed neighbouring DRC.
Judges said Ntaganda was a "key leader" of the Union of Congolese Patriots rebel group and its military wing, the Patriotic Forces for the Liberation of Congo (FPLC), in the DRC's volatile Ituri region in 2002 and 2003.