Expatriates in Australia were the first to cast their ballots followed by those in the Middle East. About 280,000 voters are registered in 14 countries.
Rebels have told voters to boycott the poll, threatening more attacks in Iraq.
Sunday’s vote will be supervised by as many as 120 international monitors, Iraqi officials say.
The head of Iraq’s independent electoral commission has said a number of foreign embassies will provide staff to act as monitors.
On Thursday ballot boxes were being put in position in southern Iraq.