It is difficult to summarise the position regarding the obligatory micro-chipping of catching Australia because the law applies on a state-by-state basis.
My understanding of it is that there are two states where it is not obligatory as yet. This is Tasmania and the Northern Territory.
If you click on the link above the picture you will be taken to a page where I discussed this matter in more detail.
Essentially, Australia is heading towards a 100% obligatory micro-chipping situation in order to better manage cat ownership and minimise the predation of domestic cats on native species which is of a major concern to the authorities.