If you are in Victoria on a temporary visa, you can drive on your overseas licence (provided it is a current, valid licence) for an indefinite period provided your overseas licence is in English (or you have an English translation), or you have an International Driving Permit.
If you are in Victoria on a permanent visa, you can drive on your overseas licence for only three months from the date you entered Victoria or from the time a permanent visa was issued to you. If you want to continue to drive in Victoria after that time you must apply for a Victorian driver licence.