The rule for a US licence
Driver licensing in Australia is a state and territory matter rather than a federal one, but the jurisdictions agree on this point: an overseas license written in English is accepted on its own. NSW states it plainly - an English translation or International Driving Permit is needed only if your license is not in English.
What does vary by state is how long a visitor may drive on an overseas license. NSW and Victoria allow six months, the Northern Territory three, and several others place no fixed limit on genuine visitors. Check the rule where you are driving if your trip is a long one.
Live in Australia?
A licence issued in Australia is what you drive on at home - an IDP translates a foreign licence, so it does not apply to you here. If your licence is from somewhere else, check that licence country: the rule depends on where the licence was issued, not only on where you are driving.
At the rental counter
Australian agencies commonly ask for the IDP where the license is not in English, and some request it regardless.
What the permit covers
An International Driving Permit is a translation of your licence into a standard multilingual booklet, issued under the 1949 and 1968 road traffic conventions. It is not a licence, and it is never valid on its own: you carry it with your own licence, and police expect to see both.
It is issued against the vehicle classes already on your home licence, and it never adds one. If your licence does not cover motorcycles, an IDP does not let you ride a scooter in Australia; if it does not cover a heavier vehicle, the permit will not cover a camper or a minibus either. The permit restates what you already hold, in a form the local authorities can read.
Driving in more than one country?
Check every destination on your trip at once - Australia is already filled in.
Check your tripOther destinations
Informational only, not legal advice. Requirements change and vary by length of stay, rental company, and vehicle class. Always confirm with the destination's embassy or your automobile association before you drive.