Saddam aides accused of torture
The 1991 Shia uprising was swiftly crushed by government forces
Kamil Abu al-Hail said he had been held at a prison in Baghdad where hundreds were beaten and tortured daily.
The defendants, including the cousin of Saddam Hussein, Ali Hassan al-Majid, are alleged to have helped suppress a Shia uprising after the 1991 Gulf War.
Tens of thousands are thought to have died in the short-lived rebellion.
In recent years, mass graves containing hundreds of bodies have been uncovered.
'Soaked with blood'
Mr Abu al-Hail was the third witness to testify against the 15 former senior military and Baath Party figures who are accused of engaging in widespread or systematic attacks against Iraq's civilian population.
The 76-year-old former Shia MP said he had been arrested after arriving in Baghdad to attend a parliamentary session in the aftermath of the uprising and taken to the nearby al-Radwaniya prison.
He told the court that Iraqi soldiers used to bring hundreds of people every day to the jail for interrogation and punishment.
"I heard screams of pain as prisoners were beaten and tortured," he said.
"At the end of the day, I could see people being carried out on blankets soaked with blood. They could not walk because of the harsh torture."
Mr Abu al-Hail said he was imprisoned even though he had not participated in the uprising. He was released several months later after receiving a presidential pardon, but said his life was destroyed.
"I was dismissed from the parliament. My cotton factory and my house were destroyed by the shelling from the army," he added.
In his opening statement at the start of the trial on Tuesday, the chief prosecutor accused the defendants of "one of the ugliest crimes ever committed against humanity in modern history".
The Shaaban Intifada (Uprising) started in March 1991 as defeated Iraqi troops fled back to southern Iraq after US-led forces took control of Kuwait.
Galvanised by a message by US President George Bush to "take matters into their own hands", Iraqi Shia rose in revolt in an attempt to topple Saddam Hussein.
But despite briefly seizing control of 14 of the country's provinces, opposition forces were swiftly crushed and mass reprisals followed.
Many Shia blame the US for the uprising's failure, as it came to a ceasefire agreement with the Iraqi government and did not intervene.Ali Hassan al-Majid, who directed Baghdad's response to the rebellion, and two more of the defendants, Sultan Hashim al-Tai and Hussein Rashid al-Tikriti, have already been sentenced to death following an earlier trial for genocide against Iraq's Kurdish population.