The Ocean of Peace Alliance was signed on Monday by Australian Prime Minister Anthony Albanese and Fijian counterpart Sitiveni Rabuka, with each country committing to come to the other's aid if they were attacked.
The text of the agreement also opened up the possibility of other Pacific nations joining.
On Thursday, New Zealand Prime Minister Christopher Luxon said the country was considering signing up to the alliance, aimed at curbing Chinese influence in the Pacific.
Foreign Minister Penny Wong said the inclusion of the trans-Tasman ally to the partnership would be a good step forward.
"We welcome the New Zealand government's interest in joining the Ocean of Peace Alliance with Australia and Fiji once it enters into force," she said in a statement.
"As Australia's longstanding ally, and a key defence partner in the Pacific, New Zealand would make a valuable contribution to the Ocean of Peace Alliance in support of regional peace and security.
"We look forward to engaging with Fiji and New Zealand in the discussions."
New Zealand's only formal alliance is with Australia, while Australia has four: New Zealand, the US, Papua New Guinea and Fiji.
The Ocean of Peace Alliance will be backed up by $1 billion to be spent over the next 10 years.
Mr Luxon said he had already spoken to his Australian and Fijian counterparts about the agreement.
"Fiji and Australia this week announced a commitment to become military allies, and New Zealand welcomes this," he said in a statement on Thursday.
"New Zealand and Australia share a close bond, with a military alliance that continues to go from strength to strength, and we also have a strong and enduring relationship with Fiji.
"We already work with both countries on how we can develop a safer region for all, so engaging with them on this alliance is logical."
A final decision on whether New Zealand commits to joining the alliance will need to be made by the country's cabinet and parliament.
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