Australia doesn't have Pre-nups as such, Instead we have what are known as Binding Financial Agreements and they can be entered into before marriage, during marriage or after marriage but before divorce. Defacto Couples can also enter into them.

However, please be warned there are specific requirements to be met before they are binding such as both parties MUST receive independent Legal Advice prior to entering.

Then even if the requirements are met there is a view in the courts that as these binding financial agreements are merely contracts, they can not be used to contract out of a persons right under the Australian Family Law Legislation.

That is the Family Law Act requires a court to make any orders it feels are just and equitable to do so. And these decisions are often made after intrinsically looking at parties relationship, length, severity as well as assets owned, contributions to the home and family etc...
It is said a BFA may be used to contract out of these rights, and so often Lawyers feel BFA's are not worth the paper they are written on as the courts are often over turning them