Many Iraqi-Kurds were hoping the tribunal will hand out the harshest possible sentence.
Salimah Bakhtiar, a Kurdish woman from the nearby city of Sulaimaniyah, lost her parents and two brothers in the campaign.
She said she planned to travel to Halabja to watch the verdict on television with relatives.
"I want to make sure all the family seeks the looks on the criminals' faces after the order to be executed is announced," she said.
Lokman Abdul-Qader, a resident of Halabja who lost six relatives in the chemical attack on the town, said he was relived the verdict was to be reached.
"Finally, the past hard days are gone. I am ready to start over without this burden on my chest."
The trial's most prominent defendant, Ali Hassan al-Majid, is a cousin of Saddam who has been called "Chemical Ali" for his alleged role in the chemical attacks.
He is the only individual, besides Saddam, to be charged with genocide over the Anfal campaign, which the prosecution says killed 180,000 people, mostly civilians.
Earlier in the trial, Al-Majid said he had the right to order the attacks.
"I am not apologising," he said. "I did not make a mistake."
The five others have been accused of war crimes and crimes against humanity in the case.
"I appeal to the UN Secretary General to quickly intervene and save the six accused from execution in the Anfal trial"
the lead defence lawyer
Although the charges carried the death penalty, Munquith al-Faroon, the chief prosecutor, had personally requested a more lenient sentence for one of the accused, Sabir al-Douri, a former military intelligence chief.
Prosecutors had also asked for another defendant Taher Tawfiq al-Ani, the former governor of Mosul, to be released because of lack of evidence.
Ahead of the judgment, the defence team approached Ban Ki-moon, the UN secretary general, to stop the trial because of "errors".
"I appeal to the UN Secretary General to quickly intervene and save the six accused from execution in the Anfal trial," Khalil al-Dulaimi, the lead defence lawyer, said in a statement.
"The six are prisoners of war and their trial by the Iraqi High Tribunal was marred by errors and violations of the law."
Human Rights Watch, a New York-based rights organisation, has also said the trial is flawed.
The rights group pointed to the the Iraqi government's removal of Abdallah al-Ameri, the first presiding judge, a few weeks after the start of the trial and and has raised concerns about "the inability of the defence to call witnesses who feared for their security".
Saddam had also been accused in the Anfal campaign, but he was executed on December 30 after he was convicted in an earlier trial for the killing of 148 people in Dujail after a 1982 attempt on his life.