Iraqis streamed into polling stations across the country to elect the first full-term parliament since the fall of Saddam Hussein in 2003.
Security was tight with searches at polling stations. Land borders and airports were closed ahead of the vote.
Iraqis had to walk to polling stations because of a blanket ban on private vehicles amid fears of car bombings.
Some 150,000 Iraqi soldiers and police officers were on patrol amid the heightened security.
Every voter had to dip a finger in ink in a bid to guard against multiple voting.
Radical cleric Moqtada Sadr has set aside bitter rivalry with other Shia leaders and joined the mainstream Shia religious list, the United Iraqi Alliance.
Turnout was reportedly high in the Sunni-dominated province of Anbar, where the electorate mostly boycotted the transitional parliament vote in January.
Most polling stations opened in the restive northern city of Mosul, despite an attack on one that killed a guard.
Some 15m Iraqis were entitled to vote in the election for a new 275-member assembly.
Women will account for a quarter of those elected to the new parliament.
Iraqi President Jalal Talabani, the country's first Kurdish head of state, was among the first to cast his ballot.