How can I work freelance in spain, whilst living in Australia

In Spain, Tax is everything, you will probably need to get a NIE number which is used in Spain for tax identification purposes for non Spanish. So what will happen as a non- resident you might need to declare tax on the money you make in Spain.

So depends on how much you make also, in Spain everything is linked to tax and its very much everywhere. You could contact a gestor and they would do all the running around for you if you need any paper work done. I am sure there may be some sort of gestor in your country so try there first before checking Spain.

I would think you would register as freelance with Australian tax authorities and pay tax there. You probably need to ask both tax authorities as there may be a withholding tax or find a Spanish tax expert. In the meantime just do the work and invoice in your name.