Anthony Albanese wrapped up the visit on Friday afternoon - the first for a prime minister since 2018 - getting agreement to wrap up talks on a security pact by the end of April.
Mr Albanese said he "hoped to have a signing in June".
Liberal frontbencher Simon Birmingham said while the engagement with PNG was welcome, it was "disappointing" the treaty was not signed on the visit.
The former coalition government began work on the treaty in 2020 with the signing of the Comprehensive Strategic and Economic Partnership.
The fourth pillar of that partnership was a bilateral security treaty which would not only address defence issues but "other common interests, including crisis and disaster management, enhanced information sharing, strengthened border management, transnational crime, cyber security and land, air and maritime security".
"While it's disappointing that treaty is not being signed on this visit, I look forward to it being signed in the coming months as per the commitment that's been made between the two governments," Senator Birmingham told reporters in Adelaide.
"We have to make sure we work as comprehensively as possible with these regional partners."
Australia's is PNG's largest trade and investment partner and provides the biggest share of development assistance.
During the trip, PNG backed Australia's bid to host the COP31 climate summit in 2026 and Mr Albanese supported a push to scale up the number of skilled and non-skilled PNG workers taking up jobs in such areas as agriculture and the care sector.
As well, a five-year program was agreed to enable more PNG women to take up leadership roles including getting elected to parliament.
Further talks are planned on law and order and policing issues, biosecurity improvements and trade, as well as a possible PNG-based team in the National Rugby League.
Mr Albanese was urged during the trip to do more to tackle climate change, with the Pacific region seen as the frontline in terms of catastrophic damage from more frequent and intense weather events.
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