Australia is a close ally of the US and was one of the first countries to send troops to the war.
It also sent military aircraft and naval vessels to the Gulf to guard Iraq's offshore oil platforms.
The 515-strong troop contingent has mainly trained and supported Iraqi forces in the Dhi Qar province.
Air Chief Marshal Angus Houston, Australia's top military commander, said in February that after the troop pullout two maritime surveillance aircraft and a warship would remain in place to help patrol Iraq's oil platforms.
He also said that a small force of security and headquarters liaison troops would remain in Iraq.
The British military spokesman said Australian civilians training the police and advising the Iraqi government would stay behind.
Meanwhile, violence continued throughout the country.
An Iraqi police checkpoint was the target of a suicide bombing west of Baghdad, with at least 13 people killed and 23 injured, police said.
Among the dead were nine policemen.
In Baghdad, a car bomb attack killed at least 2 civilians, and wounded another five.
Police say the bomb exploded in a car park used by visitors to the Iraqi ministry of defence, just outside the heavily fortified Green Zone.