It comprises a single, immense, rounded dome in the shape of a shield, formed of hardened lava from an eruption around 144 million years ago.
It covers around 310,000 square kilometres (119,000 square miles) - the equivalent area of Britain and Ireland combined - and slopes upwards to a height of around 3.5km above the sea floor.
'Tamu Massif is the largest known single, central volcano in the world,' the team reported in the journal Nature Geoscience.
In area, 'it is ... approximately the same as the British Isles or Olympus Mons on Mars, which is considered the largest volcano in the Solar System.'
It adds: 'Although Olympus Mons seems to be a giant because it is more than 20km in height, its volume is only around 25 per cent larger.'
Olympus Mons, in addition, has relatively shallow roots, whereas Tamu Massif delves some 30km into Earth's crust.
Ocean surveyors had until now surmised Tamu Massif to be a vast system of multiple volcanoes, a kind that exists in about a dozen locations around the planet.