Dutch national Frans van Anraat is accused of supplying tons of chemicals for poison gas that Hussein's military used in the 1980-88 war with Iran and against Iraq's Kurdish population, including the attack on the town of Halabja in 1988, in which an estimated 5,000 people were killed.
Van Anraat has not denied selling chemical weapons materials to Iraq, but says he was not aware of how Hussein's regime planned to use the components.
He faces a sentence of up to life in prison if convicted.
Van Anraat was first arrested in Italy in 1989 on a U.S. request but later fled to Iraq, where he is believed to have stayed until 2003 U.S.-led invasion. He was later arrested in the Netherlands.
A slideshow of photographs from Saddam Hussein's years ruling Iraq through his downfall.