US President Barack Obama hailed the elections as an 'important step forward' for the nation.
Early unofficial indicators showed turnout was around 60% as millions of Iraqis voted in a largely trouble-free environment.
Shia candidates backed by Prime Minister Nouri al-Maliki appeared to have posted gains in the polls, the nation's first election since 2005 which is also being seen as a barometer of his leadership.
'This important step forward should continue the process of Iraqis taking responsibility for their future,' Mr Obama said.
With a tight security clampdown in place across the country to guard against militant attacks, turnout was reported to be strong even in Sunni Arab insurgent strongholds or former rebel bastions.
In the 2005 parliamentary elections, turnout, excluding the three Kurdish provinces, was 49.8% as minority Sunnis massively boycotted the poll.
The UN special envoy to Iraq, Staffan de Mistura, described Saturday's turnout as 'heavy'.
