The sarcophagus had been left untouched at a university museum in Sydney for more than 150 years, the BBC reported.
When scientists opened the coffin last year, they were surprised to find the remains of human feet and bones.
Researchers said the remains were previously damaged, probably by tomb raiders.
Archaeologist Jamie Fraser said the discovery, only now made public, had been a remarkable moment.
"It was just unbelievably astonishing what we saw - one of those moments where you can't help but take in a breath and just hang in the moment," the BBC quoted Fraser, from the Nicholson Museum at the University of Sydney, as saying.
"I've never excavated an Egyptian tomb, but this comes close."
Fraser said the "dowdy-looking and non-descript" object had received little attention while Egyptologists studied the other coffins, which appeared more impressive and had complete mummies.
Experts will try to identify the mummy, which was "badly torn apart" and ransacked by tomb raiders. Only about 10 per cent of the body remains in the coffin.
Fraser said its hieroglyphics date to about 600 B.C. and show that it was built for a woman named Mer-Neith-it-es, who was either a priestess or a worshipper.
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