This total represents a substantial increase over the Australian government's 2010 figure of 6.5 million and the US Central Intelligence Agency's 2012 estimate of 6.3 million.
The once-a-decade headcount was already a year late when it started up in mid-2011.
The census received widespread criticism for failing to produce results which already impacted planning for the looming election.
PNG's Post-Courier reported on the announcement, noting a sense of pride among officials at a public declaration yesterday in Port Moresby.
"There were lots of criticisms on the conduct of the 2011 national population and housing census," national Planning Minister Sam Basil said in the PNG paper.
"However, I am now happy and convinced that the National Statistical Office has delivered this project successfully."
According to the report, the Highlands region is the most populated, with more than 3 million people, followed by the north coastal Momase region with 1.8 million.
The Autonomous Region of Bougainville received its first census numbers in 20 years, counting 234,280 people.
The Post-Courier said the National Statistical Office considered the current figure a preliminary total and expected an increased final figure to be released by 2013.