Taha Yassin Ramadan, No.20 on the US most-wanted list and Saddam Hussein's vice president, was handed over to US forces in Mosul, the US Defence Department said.
Ramadan also served on Saddam's Revolutionary Command Council member. He was Saddam's knuckles.
Chief Diane Perry at the Pentagon confirmed that he had been turned over to the US Army.
Al-Jazeera, the Qatar-based satellite broadcaster, said Ramadan was captured by troops of the Patriotic Union of Kurdistan. He was wearing peasant clothing as a disguise, the broadcaster said.
Ramadan, 65, was widely considered as ruthless as his mentor. He headed a 1970 court that executed 44 officers for plotting to overthrow the regime.
He worked as a bank clerk before Saddam's revolution. He came from the Mosul region.
Ramadan was Saddam's vice president beginning in March 1991.
During a visit to Jordan in the 1980s, Muslim fundamentalists asked Ramadan what the Baath's attitude to Islam was.
Muslims were free to pray and follow their faith, Ramadan replied, "but if they try to harm the Baathist regime or ridicule its slogans, the regime will break their necks!"
Ramadan is high on the list of regime figures Iraqi opposition groups say should be tried for war crimes.
Born in 1938, he joined the underground Baath Party in 1956 and became close to Saddam. After the 1968 coup by the party, he held several ministerial posts and became a member of the regional command in 1969.
During the 1980s, he was deputy prime minister and was for a time considered the second most powerful man in Iraq after Saddam. He remains commander of the Popular Army, the Baathist militia, but is now considered to be a secondary figure.
don said he was notified of the capture by PUK forces in a telephone call from the PUK spokesman in Sulaymaniyah.
"He was hiding among his relatives or colleagues."
In Baghdad, PUK official Kasrat Rasouli confirmed that Ramadan was captured by the PUK, but would give no other details.