Fuel cells for heavy-duty vehicles (HDVs) have attracted considerable attention because of their unique scalability, better fuel economy, the less demand for hydrogen refilling infrastructure. However, the potential application requires more stringent fuel cell durability up to 25,000 hours. Membrane electrode assemblies (MEAs) made from platinum group metal (PGM) catalyst with relatively high loading 0.3 mg_Pt/cm² play a crucial role in ensuring high-power and long-term durability. Integrating fine PGM nanoparticles and robust carbon support with strengthened interactions is critical for improving MEA performance and durability. Here, a unique atomically dispersed and nitrogen coordinated single Mn site-rich carbon (M-N-C) support was developed for high content (40 wt.%) platinum catalysts for the oxygen reduction reaction (ORR) cathode with reduced thickness. Compared with two controls studied in this work (e.g., a porous graphitic carbon-supported Pt and a commercial TKK Pt/C catalysts), the Pt (40 wt.%)/Mn-N-C catalyst exhibited much enhanced catalytic activity and stability for the ORR in both aqueous acidic electrolyte and polymer electrolyte-based MEA. We carefully elucidated the promotional role of the Mn-N-C support in promoting Pt catalyst concerning its high surface area, partially graphitic structure, and nitrogen dopants, providing better Pt nanoparticle dispersion, and strengthened interactions between Pt and carbon. Consequently, the MEA from the Pt (40 wt.%)/Mn-N-C catalyst can retain 1.2 A/cm² at 0.7 V (based on HDV conditions (0.2 mg_Pt/cm² and 250 kPa air) after 150000 voltage AST cycling. Therefore, the Mn-N-C carbon-supported Pt catalyst holds great promise to meet the challenging DOE target (1.07 A/cm² at 0.7 V after 150,000 cycles) for HDVs.