The Pukpuk agreement, named after the local word for crocodile, is slated to be signed as early as Monday by Prime Minister Anthony Albanese and PNG counterpart James Marape, who will be in Australia for Sunday's NRL grand final.
Australia is fronting up $600 million for a PNG team to join the league from 2028.
Defence Minister Richard Marles wouldn't be drawn on the timing after the prime minister was burned in September, when he was expected to ink the deal while in Port Moresby for the 50th anniversary of independence.
But he said it was "going to happen imminently".
"Let's see how it all unfolds. I just don't want to pre-empt all of that," Mr Marles told ABC Radio on Friday, when pressed on the timing of the deal.
The PNG cabinet couldn't formally greenlight the deal as ministers were away for the celebrations, meaning the signing had to be delayed and Mr Albanese returned home empty-handed.
It was the second time in a week he failed to get a Pacific nation to sign on the dotted line after Vanuatu said it needed time to review a security agreement with Australia over concerns it blocked infrastructure funding from other nations.
Former Labor defence minister Joel Fitzgibbon said while there was "a little bit of a false start", the treaty was never in doubt.
"Things work a little bit differently in PNG," he told Sky News.
PNG was significant to Australia's security, highlighted during the Second World War when it was its "last line of defence", he said.
"This is a critically important military arrangement, alliance between our two countries.
"It's mutually beneficial, but it's beneficial to peace and stability in the region.
"Deterrence really matters and this sends a very, very strong signal to others in the region."
Up to 10,000 PNG citizens could serve in Australia's military under the pact as the Pacific nation works to bolster its own military to 7000.
The pact is aimed at shoring up Australia's influence in the hotly contested Pacific region, as China tries to strike similar agreements with other island nations.
"What the treaty reflects is that Australia and PNG see their security lying in each other, and that from PNG's point of view, Australia is the natural security partner of choice," Mr Marles said.
Mr Marles opened a new maritime facility alongside Fiji's Prime Minister Sitiveni Rabuka on Friday, as the two nations strengthen defence ties and look to negotiate their own security pact.
The defence minister also met with counterpart Pio Tikoduadua.
Mr Rabuka has flagged interest in a similar deal to PNG under which citizens can serve in the Australian Defence Force.
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