The "Argyle Pink Jubilee" diamond weighs more than eight carats and is about the size of a fingernail, according to local media.
Mining giant Rio Tinto donated the gemstone to the museum where it has become part of the permanent collection.
"This diamond is very rare and incredibly large," Rio Tinto Australia Managing Director David Peever told reporters.
The diamond was discovered last August in the East Kimberley region in the north of Western Australia state, according to local media.
It was originally destined for sale at an invitation-only tender, but could only be partially cut and polished, local media reported.