Some 50,000 polling stations are operating across the country with 22 million Iraqis registered to vote.
But the process is overshadowed by violence and sectarian tension.
Dozens of people were killed in a series of blasts at an election rally last Friday.
Extra security forces are deployed, checkpoints are manned on street corners throughout the capital.
In spite of increased violence, many people appear optimistic for a peaceful future.
“We do not want this life, we are against what is happening, against these explosions,” said one Iraqi woman. “I hope God will stop them, so that we can live peacefully.”
An Iraqi man commented: “These elections are a new union between Iraq and the Iraqis. We want to change our situation so that Iraq continues on a good path and we do not go back.”
Nickolay Mladenov, the United Nations envoy to Iraq, urged people to vote to make sure they have a say in the future of their country.
“The Iraqi high election commission has prepared very professionally to conduct the poll today,” he told reporters at a polling station outside the Green Zone in central Baghdad. “They have a lot of capacity and should be trusted by all the political forces in this country that they will do their best job to ensure that the election is conducted in a proper manner,” Mladenov added.
Euronews correspondent Muhammed Shaikibrahim in Baghdad reported from in front of a polling station: “There are mixed feelings here today. People want a better future, but many are afraid of violence, of being attacked when they show up to vote. Iraqis want a change, but the political uncertainty and not knowing how these elections will pan out are making people weary.”