Awad Hamad al-Bandar, who oversaw the trial of 148 Shia men convicted in the assassination plot in 1982, said in court on Monday that he personally issued a death warrant for them and insisted that it was legal.
"They attacked the president of the republic and they confessed," al-Bandar said in testimony before the judges trying him, Saddam, and six others for crimes against humanity.
Al-Bandar, the first of the four senior defendants to give testimony in his own defence, accused the dead men of being part of a plot by the Iranian-backed Dawa party to kill Saddam during Iraq's war with Iran.
"It was provoked by Iran. They were members of Dawa. The leadership of Dawa was in Iran," al-Bandar said.
The present leader of Dawa, a Shia Islamist party, is Ibrahim al-Jaafari, the Iraqi prime minister whose government has pressed for the Dujail trial to be conducted swiftly.
"The target was the head of state and we were in a state of war with Iran," al-Bandar said.
"It was provoked by Iran. They were members of Dawa. The leadership of Dawa was in Iran"
Awad Hamad al-Bandar, former head of Iraq's Revolutionary Court
"He [Saddam] was the commander of the armed forces.
"The court took two weeks. The 148 men had confessed. It is all in the files."
The killing of the men from the Shia town of Dujail is at the heart of the case.
Taha Yasin Ramadan, the former Iraqi vice president, who is also accused in the Dujail case, said he was tortured by his interrogators.
Ramadan told the court plaided not guilty of all the charges raised against him and reaffirmed that Saddam did not give the 148 men in Dujail.
Saddam said on 1 March that he had ordered the trial under al-Bandar which led to the executions, and said this had been an entirely legitimate procedure.
He also said farms had been razed around the town in reprisal.
In a phase of the trial that began on Sunday, four local Baath party officials from Dujail had already made their appearances.
Three of them contested sworn statements the prosecution said they had made in pre-trial proceedings.