Bryce Barker, who now lives in Australia, was held alongside fellow members of his research team.
They were doing fieldwork in a remote part of PNG's highlands when they were taken by a criminal gang from Hela Province who demanded a ransom for their freedom.
Their release brings to an end days of negotiations, and a complex security operation involving PNG police and defence personnel, in consultation with the Australian and New Zealand governments.
It comes two days after another woman who had also been taken was set free.