US President George W Bush hailed the conviction of Saddam for crimes against humanity as a "major achievement" and a "milestone" for Iraq's move to democracy.
"The trial is a milestone in the Iraqi people's efforts to replace the rule of a tyrant with the rule of law," Mr Bush said.
The US ambassador in Baghdad said the ruling marked an "important milestone" for the war-torn country.
"A former dictator feared by millions, who killed his own citizens without mercy or justice, who waged wars against neighbouring countries, has been brought to trial in his own country -- held accountable in a court of law with ordinary citizens bearing witness," Ambassador Zalmay Khalilzad said.
Britain said it was right Saddam had been "held to account" for his crimes after he was sentenced to death for his role in ordering the deaths of 148 Shiite villagers in the village of Dujail, north of Baghdad.
Iraqi Prime Minister Nuri al-Maliki hailed the verdict -- declaring "Iraq's martyrs can now smile again".
But there were doubts over the death penalty imposed on Saddam and two of his senior aides.
The Finnish presidency of the European Union on Sunday called in a statement for Iraq not to use the death penalty against Saddam.
"The EU opposes capital punishment in all cases and under all circumstances and it should not be carried out in this case either," the statement said.
"Over the years, the European Union repeatedly condemned the systematic, widespread and extremely grave violations of human rights and of international humanitarian law committed by the regime of Saddam Hussein," it added.
In Italy, Prime Minister Romano Prodi said Saddam's death sentence reflected the international community's judgement of the former Iraqi leader, even as he expressed misgivings about the sentence.
"As much as the crime appals us, our traditions and our ethics distance us from the use of the death penalty," Mr Prodi said, in remarks quoted by the ANSA news agency.
A similar mix of satisfaction and unease was reflected in statements from Sweden, Spain, Denmark and Ireland.
"Like any other political leader, Saddam Hussein should answer for his actions," Spain's Socialist Prime Minister Jose Luis Rodriguez Zapatero told reporters in Uruguay, where he is attending an Ibero-American summit.
"But the death penalty is not envisaged by any European Union procedure and is not well understood in our country," he added.
And while Danish Foreign Minister Per Stig Moeller saluted Iraq for conducting the trial in "an independent manner", he expressed reservations about the special tribunal that judged Saddam.
"In the case of Denmark, we don't support this special tribunal," said Mr Moeller, whose country has 470 soldiers deployed in Iraq, mostly under British command.
Amnesty International described the trial as a "shabby affair, marred by serious flaws", while Human Rights Watch said it should have been conducted by an international court and labelled it a "lost opportunity to give a sense of the rule of law".
UN human rights chief Louise Arbour called for a moratorium on executions and said the rights of the defendants to a fair appeal must be "fully respected".
France, one of the main opponents of the 2003 US-led invasion to topple Saddam, said it hoped already bloody sectarian strife in Iraq would not worsen as a result of the death sentence.
In Moscow, Konstantin Kosachev, president of the parliamentary commission for foreign affairs, warned of "catastrophic consequences" in Iraq if Saddam were hanged, but expressed scepticism that the death penalty would be carried out.
In Iran which is still bears the scars of the 1980-1988 war against Iraq there was a sense of relief and jubilation that an arch-foe had finally had his come-uppance.
The ruling Palestinian Islamist movement Hamas, on the other hand, condemned the death sentence, recalling the financial help the deposed Iraqi leader gave to the Palestinian people after the intifada broke out in September 2000.
India reacted guardedly saying the death sentence required the "credible due process of law".
Nigeria's highest Islamic body Sunday said that while it agreed that Saddam
Hussein was a "terrible man", it was not sure if the atmosphere in which he was tried was "conducive" for due process.
A senior Vatican official lamented the death penalty imposed on Saddam, suggesting it marked a vengeful "eye for an eye" mentality still gripping turmoil-torn Iraq.
"Iraq is among those countries which haven't yet made the civilized choice of abolishing the death penalty," said Cardinal Renato Raffaele Martino, president of the Pontifical Council for Justice and Peace, according to the ANSA news agency.
"Today, modern society has all the means to render harmless someone who has committed a crime without recourse to the death penalty,"
If Saddam had been tried by the International Criminal Court, he added, "he never would have been sentenced to death" since the body specifically excludes the death penalty for crimes against humanity or other offences.