The agency's space explorer, the Curiosity rover, has snapped what may be trace fossils created by soft-bodied creatures on the red planet, he says.
An upcoming 'bombshell' report will reveal how Nasa is aware of the find and has chosen to keep it hidden from the public, the scientist claims.
The controversial scientist believes the space agency could be ignoring the find because of its plans for a manned mission in the 2030s, when astronauts will explore Mars in more depth.
However, according to Nasa, the shapes captured in images from Mars are simply rock crystals that are currently undergoing analysis.
The findings were made by Barry DiGregorio, an honorary research fellow at the University of Buckingham who specialises in studies of microscopic life found in the soil of our planet.
Images beamed back from Mars by Curiosity appear to show patterns similar to Ordovician trace fossils Dr DiGregorio has photographed here on Earth, he says.