Kenya has shown little willingness to prosecute those responsible for the violence, but has agreed to provide the ICC with confidential information about the incidents.
"President [Mwai] Kibaki's and Prime Minister [Raila] Odinga's commitment to justice and to co-operation with the ICC is crucial," Ocampo said after a three-judge panel authorised him to investigate.
"This is a moment for Kenyans to come together," he said.
"To understand and acknowledge what happened. To make sure it will never happen again."
Mark Ellis, the executive director at the International Bar Association, welcomed the decision.
"I think it is a very important step for Kenya and the international community," he told Al Jazeera.
"The ICC provided an opportunity for Kenya to undertake their own investigation and prosecution, but they were not able to do that.
"It is morally and legally right for the International Criminal Court now to undertake this first step and that is the investigation into the crimes that were committed in Kenya."
Ellis said that Kenyans cannot enjoy "sustainable peace and certainly not reconciliation" unless those who have committed the atrocities are brought to justice.
The ICC is the world's first permanent court mandated to bring to justice perpetrators of war crimes, crimes against humanity, and genocide when national courts are unable or unwilling to do so.
Currently, 110 states are parties to the ICC.