Bush administration officials have identified al-Zubaydi as one of nine Iraqis — including Saddam himself — sought for trial on charges of war crimes or crimes against humanity.
A nurse by training and former member of Iraq's ruling Revolutionary Command Council and regional commander of the central Euphrates district, al-Zubaydi was No. 18 on a list of the 55 most-wanted figures from the Saddam's regime. Iraqi opposition groups have accused him of the 1999 assassination of a top Shiite cleric.
"This is very significant — he is one of the most hated men in the former regime," said Haider Ahmad, a London-based spokesman for the Iraqi National Congress, one of the numerous parties that, in exile, had opposed Saddam's government.
Al-Zubaydi was an associate of Saddam since the early 1960s and had been retired from a public role in the leadership for about two years.
Central Command gave no further details on his arrest. The Iraqi National Congress, the leading anti-Saddam organization, said its forces arrested al-Zubaydi in Hillah, about 60 miles south of Baghdad, and turned him over to U.S. forces.
Ahmad said local people tipped forces to where al-Zubaydi was hiding with his son, and that the two were caught together.
"He was hiding in an abandoned, derelict area, not a built-up area," he said.
With Monday's capture, eight of the 55 most wanted are now in custody, though none of them is from the very top of the list. A ninth figure, Ali Hassan al-Majid — a top adviser to Saddam and known as "Chemical Ali" for his use of poison gas against Iraq's Kurdish minority — is believed to have been killed in an airstrike in Basra.
Al-Zubaydi, a former prime minister and deputy prime minister, was one of the key figures in suppressing the uprising of Iraq's Shiite majority that followed Iraq's defeat in the 1991 Gulf War. Tens of thousands of people died.
Al-Zubaydi was considered one of the most brutal members of Saddam's regime and was listed in a U.S. State Department report "Iraq: Crimes against Humanity, Leaders as Executioners." He was once featured in an Iraqi videotape brutalizing Shiite dissidents as a display of authority and encouragement to soldiers to be tough.
A Shiite himself, al-Zubaydi also presided over the destruction of the southern marshes in the 1990s, an action aimed against Shiite "Marsh Arabs" living there.
The marshes — roughly 3,200 square miles — had provided the necessities of life for tens of thousands of Arab marsh dwellers for at least 1,000 years. They were destroyed through a large-scale water diversion project aimed at removing the ability of insurgents to hide there.
Al-Zubaydi served as prime minister from 1991 to 1993; as deputy prime minister from 1994; and as commander of Central Euphrates Region from 1998 to 2000. He was dismissed in 2001 as deputy prime minister and from the Baath Party Regional Command.
Iraqi opposition groups have accused him of assassinating Grand Ayatollah Mohammed Sadeq al-Sadr and his two sons in the holy city of Najaf in 1999.
Al-Zubaydi himself escaped several assassination attempts in the years following 1991.
He is the queen of spades in the deck of Saddam's henchmen distributed to U.S. forces. Saddam tops the list and was designated the ace of spades.
It was the second time in as many days the Iraqi National Congress was credited with detaining most-wanted figures.
On Sunday, the congress said Saddam's son-in-law, Jamal Mustafa Abdallah Sultan al-Tikriti, and one of Saddam's bodyguards, came out of hiding in Syria and surrendered to the group.
The INC said Monday it believed Saddam was alive and was tracking him and son Qusay, receiving word of their movements 12 to 24 hours after they occurred.
Iraq's minister of higher education and scientific research, Abd al-Khaliq Abd al-Gafar, was apprehended on Saturday.
Other top arrests by coalition forces include Watban and Barzan Ibrahim Hasan al-Tikriti, two of Saddam's three half brothers; Hikmat Mizban Ibrahim al-Azzawi, the finance minister and deputy prime minister; science adviser Lt. Gen. Amer al-Saadi; and Samir Abd al-Aziz al-Najim, a senior figure in Saddam's Baath Party.
U.S. officials have hinted that other leaders might be in custody.