Leeth v Commonwealth,[1] is a High Court of Australia case that held that there was no implied right of legal equality in the Australian Constitution.

Mason CJ, Dawson and McHugh JJ denied that the Constitution contained an implied right to substantive legal equality, and only recognised procedural inequality.

However, Brennan J did not agree that the right had been violated, and thus there was a majority for the outcome that the Act was not invalid.

The basis for the implied right of substantive equality (as advocated by Deane and Toohey JJ) comes from the fact that the constitution is a free agreement between the people of the colonies, and these pre-existing rights continued after federation.

In the absence of words that deny such equality, these pre-existing rights should continue to exist.