The verdicts against Saddam Hussein and his co-defendants mark an "important milestone" for Iraq and demonstrate the "commitment of the Iraqi people to hold them accountable", US ambassador Zalmay Khalilzad said on Sunday.
"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," the ambassador said in a statement.
Saddam and two of his senior allies were sentenced to death by hanging after an Iraqi court found them guilty of crimes against humanity.
Saddam's half-brother and intelligence chief Barzan al-Tikriti was also sentenced to death, as was Awad Ahmed al-Bandar, who was convicted as the president of the kangaroo court which ordered the Shiites executed.
Former vice president Taha Yassin Ramadan received a life sentence, while three Baath party officials from Dujail received 15 years each.