We propose a novel, facile synthesis route to produce stable platinum-based polymer electrolyte membrane fuel cell catalysts supported on nitrogen-doped carbon. Platinum nanoparticles were decorated on polyaniline (PANI), a nitrogen-containing polymer, before its subsequent carbonization at 750 °C under nitrogen atmosphere. Thus, nitrogen-doped carbon-supported platinum catalysts were produced with homogeneously distributed small metal particles, which are otherwise difficult to obtain. Most remarkably the platinum nanoparticles did not grow significantly during the carbonization step. In contrast, commercially available standard catalysts on carbon materials subjected to the same heat treatment showed severe particle growth. In accordance with the high thermal stability, the PANI-derived catalyst shows good long-term stability in accelerated stress test and a promising performance as cathode material in 5 × 5 cm2 single cells. The synthesis is carried out without the need for special laboratory equipment, so it will be easy to scale up for industrial catalyst production.