Former Iraqi president Saddam Hussein's cousin Ali Hassan al-Majid was executed on Monday, according to the government.
"The condemned... has been executed by hanging today," government spokesman Ali al-Dabbagh announced on state television.
"This penalty is just retribution for the offender."
Al-Majid, dubbed "Chemical Ali" for ordering the use of chemical weapons against Iraqi Kurds in the village of Halabja in 1988, was sentenced to death last week for the attack.
On March 16, 1988, a day Iraqis remember as "Black Friday," Iraqi warplanes sprayed the village with mustard gas, Sarin, Tabun, and VX gas, killing at least 3,200, injuring at least 7,000 more, and causing birth defects for years to come.
Al-Majid was among the architects of the broader Anfal campaign against Iraq's Kurds that killed as many as 100,000 people.