You are not able to drive using the overseas licence, even when you put the P-Plate. You need to be authorised to drive in Australia by going through the Australian system, overseas licences are not authorised in Australia, there maybe a legal approval to use it for few months as this is to assist someone coming new to Australia, knowing they need time to settle, the other option to use the overseas licence is to obtain an International Licence from the issuing country of your licence and make sure that the Int. licence includes Australia.
If you drive using the overseas licence and use the P-Plate, then you are breaking several laws and you will get hefty fines. So start with your Australian licence process.