This is the first time an ichthyosaur fossil has been discovered in India.
The fossil was found inside rocks from the Mesozoic Era, which ran between 252 and 66 million years ago, in the Kutch desert.
Prof Guntupalli VR Prasad, who led the study, said the 5.5m (18ft) specimen was almost complete.
Only parts of the skull and tail bones were found to be missing.
The findings have been published in the Plos One science journal.
“This is a remarkable discovery not only because it is the first Jurassic ichthyosaur record from India, but also it throws light on the evolution and diversity of ichthyosaurs in the Indo-Madagascan region and India’s biological connectivity with other continents in the Jurassic,” Mr Prasad said.
The team, which comprised scientists from India and Germany, believes the newly discovered specimen can be identified with Ophthalmosauridae, a family of ichthyosaurs that lived in the oceans between 165 and 90 million years ago.