The team from Australia's national science agency (CSIRO) made the discovery during a search for larval lobster breeding grounds.
The cluster of volcanoes is believed to be around 50 million years old.
The researchers say the discovery may hold clues to how Australia separated from New Zealand.
The volcanoes were discovered about 250km (155 miles) off the coast of Sydney.
"This is the first time these volcanoes have been seen," volcano expert Richard Arculus told AFP.
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