The 65-feet-tall new species of titanosaur, 130 feet in length and weighing 77 tonnes, is much heavier than the previous record holder Argentinosaurus, palaeontologists said.
The remains of the enormous herbivore dating from the Late Cretaceous period were first discovered by a local farm worker in the desert near La Flecha, about 250km west of Patagonia, the 'BBC News' reported.
Scientists from the Museum of Palaeontology Egidio Feruglio, led by Dr Jose Luis Carballido and Dr Diego Pol, then excavated the fossilised bones.
The palaeontologists unearthed the partial skeletons of seven individuals - about 150 bones in total - all in "remarkable condition".
"Given the size of these bones, which surpass any of the previously known giant animals, the new dinosaur is the largest animal known that walked on Earth," researchers said.
"Its length, from its head to the tip of its tail, was 40 metres. Standing with its neck up, it was about 20 metre high - equal to a seven-storey building," they said.
The giant herbivore lived in the forests of Patagonia between 95 and 100 million years ago, based on the age of the rocks in which its bones were found.
However, despite its magnitude, it does not yet have a name, the report said.
"It will be named describing its magnificence and in honour to both the region and the farm owners who alerted us about the discovery," researchers said.
The most recent pretender to the 'biggest dinosaur' throne was Argentinosaurus, a similar type of sauropod, also discovered in Patagonia that weighs about 70 tonnes.