The execution of Ali Hassan al-Majeed is to go ahead after Iraq's Presidency Council approved the penalty.
The council, made up of President Jalal Talabani and his two deputies, has for months blocked the execution of al-Majeed and two others.
They were convicted last June of a campaign of genocide against Iraqi Kurds in the 1980s, including the Anfal military campaign in 1988 when the population of Halabjah was killed with poison gas.
That attack earned al-Majeed the nickname 'Chemical Ali'.
While the council was not against hanging al-Majeed, there was disagreement over whether his two co-accused, former defence minister Sultan Hashem and former army commander Hussein Rashid Muhammed, should suffer the same fate.
It will be up to Prime Minister Nuri al-Maliki's government to set a date for the death sentence to be carried out.
The US military, which has custody of al-Majeed and other former members of Saddam's government, said it had not received a request to hand him over to the Iraqi authorities, which would signal that his execution was imminent.
A source at the presidency council said no decision had been made regarding the fate of Hashem and Muhammed.
Catholic archbishop kidnapped in Mosul
A Chaldean Catholic archbishop has been kidnapped by gunmen in Iraq's restive northern city of Mosul after a shootout that killed his three companions.
Faraj-Farraj Rahhu, the archbishop of Mosul, was kidnapped after a shootout in the eastern Nur district of the city. Two bodyguards and his driver were killed.
Pope Benedict XVI swiftly condemned the kidnapping as an 'atrocious act which touches the whole of the church' in Iraq.
