The European Union plans to reach net-zero greenhouse gas (GHG) emissions in 2050. In 2020, the transport sector significantly contributed to global energy-related GHG emissions, with heavy-duty vehicles (HDVs) responsible for a substantial portion of road transport emissions in the EU and a notable percentage of the EU’s total GHG emissions. Zero-emission vehicles (ZEVs), including fuel cell (FC) vehicles, are crucial for decarbonizing the transport sector to achieve climate neutrality. This paper aims at quantifying the environmental impacts of a 200kW proton exchange membrane FC system for long-haul HDVs with a 40-ton mass and 750 km driving range. The life cycle assessment (LCA) methodology was applied, and a life cycle model of the FC system was developed with a cradle-to-grave boundary. To ensure reproducibility and scalability, results are reported on a kW basis. A sensitivity analysis was performed on key parameters, including hydrogen production route, FC system production location, fuel consumption, FC system size, FC system replacement, and FC material composition. At the cradle-to-gate boundary, GHG emissions of the FC system ranged from 30.5 to 51.4 kg CO₂eq/kW. The catalyst was the most impactful component due to the presence of platinum, followed by the balance of plant. In the cradle-to-grave boundary, raw material extraction and production phases were negligible, while the use phase was the main driver of the overall impact of the FC system. Certain equivalences were observed when considering other impact categories.