Hospital staff including the sick, and prisoners with less than five years left in jail are also eligible to vote on Thursday in their places of work or detention.
First few votes
Nidhal, a nurse at Baghdad's Abid al-Haitham hospital, would not reveal the name of the candidate she had voted for, but hinted that "he is secular".
A full-scale security clampdown is being rolled out in Iraq ahead of regional elections
Her finger bore an ink stain, indicating she had cast her ballot.
"I hope deep down in my heart that he will win, because Iraq cannot be governed by Islamists and we need a saviour."
Almost 19 million Iraqis, from a population of 30 million, are eligible to vote at 10,000 polling stations around the country, with 6,200 candidates standing for the 325 seats in parliament.
Iraqi expatriates will begin voting in 80 cities across 16 countrieson Friday, a process that will continue until Sunday.
Iraq's electoral commission says 1.4 million people are eligible to vote abroad.
Al Jazeera's Mike Hanna, reporting from Baghdad, said the vote is seen as a pivotal moment in Iraq as the US prepares to withdraw large numbers of troops by 2011.
"This is a very significant vote; it is the closest to a truly representative process since the US-led invasion [in 2003].
"A short while ago an explosive device was detonated at a polling station northeast of Baghdad - that is not being used by the early voters today - but one that will be used in the election on Sunday.
"However, police say the damage was minimal. At this stage not a significant event but a reminder of how dangerous this election process can be," he said.
More than 6,000 candidates will be competing for 325 seats in the election.
Travel around the country has been restricted and the authorities have cancelled all leave for security services.
The election winners will oversee the withdrawal of US forces from the country and help determine whether Iraq will be able to move past the deep Sunni-Shia divisions that almost destroyed it.
Five years ago, Iraq's Sunni Arabs boycotted the legislative election,allowing Shia and Kurdish parties to take control of parliament, but Sunnis are now expected to take part in large numbers.