At least 3,000 people were killed and more than 100 others raped during violence when Gbagbo refused to accept defeat as a result of the Oct. 31, 2010, presidential election, Moreno-Ocampo said.
More than 500 others were arbitrarily detained, he said.
After getting the OK, Moreno-Ocampo said he would send investigators to the western African country Monday.
Gbagbo clung to power, refusing to cede to former Prime Minister Ouattara and using security forces to terrorize citizens in the former capital of Abidjan where Ouattara was holed up.
The international community -- including the United Nations, African Union, European Union and United States -- said Ouattara won decisively. Gbagbo charged massive voter fraud.
After international organizations reported numerous human rights violations, the United Nations and former colonial power France began military action with the stated objective to protect itself and civilians.
Gbagbo was captured in Abidjan by pro-Ouattara forces backed by French forces.
Ouattara took office May 6 and asked the international court to investigate crimes committed by both sides during the crisis.
The Italian group No Peace Without Justice applauded the investigation but said Moreno-Ocampo should look as far back as the country's 2002 civil war.