The 300 is not the destination. It is the entry visa that lets you marry in Australia, then transition to the permanent partner pathway.
Enter AustraliaTravel to Australia once the 300 is granted. Visa valid for a specific period, usually 9 to 15 months from grant, during which the marriage must take place.
Full work and study rightsThe 300 holder has full work and study rights from arrival. No restrictions.
Get marriedThe marriage must happen within the validity period. Registry ceremony, religious ceremony, or any other legally recognised Australian marriage.
Apply for the 820/801After the marriage, the applicant applies for the Subclass 820 onshore partner visa. The 820 must be lodged while the 300 is still valid or shortly after, and the applicant must be in Australia.
Continue to permanent residency820 granted first (temporary), then 801 around 2 years later (permanent). Same evidence rules as any other partner visa.