The Czech-born chemist who moved to England in 1938 was 85 and had suffered from Parkinson's disease for years before his death Friday, the BBC reported.
The "cold fusion" claim of Fleischmann and Pons ignited a scientific firestorm, as researchers around the world attempted to replicate the duo's simple experiment that seemed to promise almost unlimited cheap energy.
The results were never duplicated, however, and the concept of fusion in normal laboratory conditions is now almost completely discredited.
Fleischmann was working with Pons, an American scientist, at the University of Utah when their controversial experiment was carried out.
Amid accusations of "sloppy" work or even outright fraud, the pair moved to France to continue experiments meant to validate their claims, while the idea of cold fusion was relegated to the realm of "fringe" science.
Fleischmann returned to England in 1995 and became increasingly distant from the small research community still attempting to recreate the initial findings, the BBC said.
Wisconsin business offering 'therapeutic cuddling' forced to close
Britney Spears debuts 'Perfume' video