Figures compiled by the health, interior and defence ministries put the death toll at 15,538, compared with 17,956 killed in 2007, during the height of Sunni-Shiite sectarian killings.
The toll was also more than double the 6,522 people killed in 2013.
The year got off to a bloody start, with the government losing control of parts of Anbar provincial capital Ramadi and all of Fallujah - just a short drive from Baghdad - to anti-government fighters.
It spread to Fallujah, and security forces later withdrew from areas of both cities, leaving them open for capture.
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That was a harbinger of events of June, when the Islamic State group spearheaded a major jihadist offensive, sweeping security forces aside.
The militants overran Iraq's second city Mosul and then drove south toward Baghdad, raising fears the capital itself would be attacked.
They were eventually stopped short, but seized swathes of five provinces north and west of the capital.
That effort has since been expanded to training Iraqi forces aimed at readying them as quickly as possible to join the fight against IS.
Iraqi soldiers and police, Kurdish forces, Shiite militias and Sunni tribesmen have succeeded in regaining some ground from IS.
But large parts of the country, including three major cities, remain outside Baghdad's control.