Two families on holiday unearthed the prehistoric predator at a free fossil-finding site in north-west Queensland.
The remains are thought to be from the Australopachycormus hurleyi, a 3m-long ray-finned fish with a pointed snout.
"Part of what makes this specimen so special is that it is so complete," Dr Patrick Smith told the BBC.
The curator of Kronosaurus Korner says that the centre has assembled the ancient creature's skull, backbone and fins.
"We know that it was a high-tier carnivore and that it ate other large fast-moving fish, a bit like marlin do today," he said.
"Because it does fit that swordfish-like shape we know he probably lived in that same ecological niche."
Dr Smith said he wanted to encourage other amateur palaeontologists to make their way to the tiny outback township 1,700km (1,000 miles) from Brisbane.
"Come to Richmond, because there's an awful lot of material to be collected," he said.
Fossils have been turning up since the 1930s in the region of north-west Queensland, which is described as "Australia's Dinosaur Trail".
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"Extremely rare" fossils from a swordfish-like creature which lived 100 million years ago have been discovered in the Australian outback.