The registration period will now close at 7pm (0900 GMT) on Tuesday, Bernie Hogan of the International Organisation for Migration (IOM) said, after only 6500 people registered between Monday and Friday.
Organisers had originally predicted that up to 40,000 of an Australian Iraqi exile community estimated at around 90,000 would turn up to register.
Announcing the extension late on Saturday, Hogan admitted the turnout was disappointing but said it had been mirrored by low registration turnouts around the world.
"We're disappointed and the Iraqi leaders in the community are incredibly disappointed," he said. "There is a frustration generally that we're not getting the numbers we expected.
"Everybody in the world is quite stunned with the low turnout
Australia's Iraqi exile community
is estimated at around 90,000
for registration. This is a golden opportunity for Iraqi people to have a say in the future of their country and I can only exhort them to register and vote."
The organisation of the process in Australia has come in for criticism. Registration centres have been set up only in the major cities of Perth and Melbourne, plus the remote community of Shepparton in Victoria state which is home to a large number of Iraqis.
This has meant about 9000 Iraqis in Western Australia state have to travel at least 250km if they want to vote.
Fear of deportation
Hogan said some Iraqis feared the Australian government would seize their registration data and seek reasons to deport them, while others were concerned about the information being seized by a future Iraqi government and used against family members back home.
Some also felt the result was a foregone conclusion and it was pointless to vote as US-backed interim Prime Minister Iyad Allawi would inevitably get returned to office.
Australia is one of 14 countries in which the International Organisation for Migration has said that expatriate Iraqis wishing to register at voting centres for the 30 January poll could have an extra two days in which to do so.