Former Iraqi Vice-President Taha Yassin Ramadan has been hanged on the fourth anniversary of the US-led invasion which overthrew Saddam Hussein.
Ramadan was originally jailed for life over the Dujail killings
The execution happened before dawn at a prison in northern Baghdad. An Iraqi official said it had gone smoothly.
One of Saddam Hussein's co-defendants, he was sentenced to life for his role in killing Shias in the 1980s, but his punishment was increased at an appeal.
The execution was described as "a political assassination" by his son.
Ahmad Ramadan was speaking to al-Jazeera TV from the Yemeni capital, Sanaa.
He said his father would be buried in or near the Iraqi city of Tikrit, near Saddam's burial place.
Ramadan, who was thought to be in his late 60s, was the third senior former official to be hanged since Saddam Hussein was executed on 30 December. All were found guilty of crimes against humanity.
Two of Saddam Hussein's former aides, Barzan Ibrahim al-Tikriti and Awad Ahmed Bandar, were put to death on 15 January.
The official said care was taken to avoid a repeat of Tikriti's bungled execution, which led to the condemned man being decapitated during the hanging.
"The execution was smooth with no violation," he said.
TAHA YASSIN RAMADAN
Born to peasant family near Mosul, northern Iraq
Took part in 1968 coup that put Baath party into power
Became vice president in 1991
He said officials from the prime minister's office and the justice ministry were present at the hanging, along with a doctor, a prosecutor, a judge and a lawyer representing Ramadan.
Ramadan had said he had no fear of death and that he would "die bravely", according to his lawyer.
He was held in US custody until shortly before the execution, when he was handed over to Iraqi authorities.
The sentence was carried out at a prison on a military base in northern Baghdad, an official said.
Ramadan had maintained his innocence throughout the legal proceedings.
He was convicted along with the deposed Iraqi leader and others over their part in the killing of 148 Shias in the town of Dujail in the 1980s, in apparent revenge following a failed assassination attempt against Saddam Hussein.
Ramadan, who was born in the late 1930s, lost his final appeal last week and under Iraqi law had to go to the gallows within 30 days.
He was captured by Kurdish fighters in the northern city of Mosul in August 2003 and handed over to US forces.