Do I have to be outside Australia to apply for a Transit visa?

The Transit visa is an offshore visa. You need to be outside Australia both when you apply and when the visa is decided, since its whole purpose is to authorise your arrival for a brief transit.

This means you should apply with enough time before travel for the visa to be granted before you reach Australia. Arriving without the required transit authority can lead to being refused entry.

Make sure your passport and travel documents are valid and that your onward arrangements are confirmed, as these support both your eligibility and a smooth transit.