Queues formed from early morning at tightly-guarded election centres despite a surge of violence targeting polling stations and campaign gatherings in the days leading up to the vote.
The stream of voters slowed later in the morning but the tempo was expected to pick up again in the afternoon before polls close at 6:00 pm (local time).
Iraqis have a long list of grievances, from poor public services to rampant corruption and high unemployment, but the month-long campaign has centred on Maliki's bid for a third term and dramatically deteriorating security.
Maliki encouraged voters to turn out in large numbers and voiced confidence he would return to power after casting his ballot at a VIP polling centre set up in the Rasheed Hotel in Baghdad's heavily-fortified Green Zone.
"Today is a big success, and even better than the last elections, even though there is no foreign soldier on Iraqi soil," the premier said.
He called for a move away from national unity governments to ones of political majority, and confidently told journalists, "Our victory is certain, but we are waiting to see the size of our victory."
The run-up to the election, the first since US forces departed in December 2011, has seen Baghdad and other major cities swamped in posters and bunting.
Parties have staged rallies and candidates have angrily debated on television, though appeals to voters have largely been made on sectarian, ethnic or tribal grounds rather than on political and social issues. Analysts had voiced fears that much of the electorate would stay home rather than risk being targeted by militants, who in the past two days killed nearly 90 people.
Fresh attacks which left two women dead and two other people wounded were launched soon after voting began on Wednesday.


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