The 1992 Mabo decision was the landmark High Court decision that overturned the doctrine of terra nullius. The Court recognised native title based on possessory title by reason of long possession.
Akin to the laws of adverse possession, the decision was based on the findings of fact of evidence of Murray Island people (Mer Islanders) had a strong sense of relationship to the islands and regarded the land as theirs.
All of the judges, except Justice Dawson, agreed that:
- there was a concept of native title at common law;
- the source of native title was the traditional connection to or occupation of the land;
- the nature and content of native title was determined by the character of the connection or occupation under traditional laws or customs; and
- native title could be extinguished by the valid exercise of governmental powers provided a clear and plain intention to do so was manifest and consecutive.
- Rejection of terra nullius: The decision recognised that the indigenous population had a pre-existing system of law, which, along with all rights subsisting thereunder, would remain in force under the new sovereign except where specifically modified or extinguished by legislative or executive action. The Court purported to achieve all this without altering the traditional assumption that the Australian land mass was “settled”. Instead, the rules for a “settled” colony were said to be assimilated to the rules for a “conquered” colony.
- Fragmentation of proprietary interests: Justice Toohey made the argument that common law possessory title could form the basis for native title claims by indigenous Australians. This has not subsequently been pursued.