Your result
Australia — Marriage
Possible
Everything starts with your partner's status, because it is their status that creates the sponsorship, and the distinction that matters is one couples frequently blur.
An Australian citizen can sponsor. An Australian permanent resident can sponsor. An eligible New Zealand citizen can sponsor. Someone who has lived in Australia for many years on temporary visas cannot, however settled they look — and someone born in Australia is a citizen whether or not they have ever held an Australian passport. The gap between permanent residence and citizenship also matters less here than people expect: a permanent resident can sponsor you just as a citizen can.
Your partner can establish their own status through the Department of Home Affairs' visa entitlement verification service, which reports what they hold. If they were born in Australia, or had an Australian parent, and have simply never documented it, an application for evidence of Australian citizenship will settle it and may reveal that they have been a citizen all along.
Once you know which of those applies, the rest of the partner visa question becomes answerable.