Hydrogen leakage in Proton Exchange Membrane (PEM) fuel cells poses critical safety, efficiency, and operational reliability risks. This study introduces an innovative infrared (IR) thermography-based methodology for detecting and quantifying hydrogen leaks towards the outside of PEM fuel cells. The proposed method leverages the catalytic properties of a membrane electrode assembly (MEA) as an active thermal tracer, facilitating real-time visualisation and assessment of hydrogen leaks. Experimental tests were conducted on a single-cell PEM fuel cell equipped with intact and defective gaskets to evaluate the method’s effectiveness. Results indicate that the active tracer generates distinct thermal signatures proportional to the leakage rate, overcoming the limitations of hydrogen’s low IR emissivity. Comparative analysis with passive tracers and baseline configurations highlights the active tracer-based approach’s superior positional accuracy and sensitivity. Additionally, the method aligns detected thermal anomalies with defect locations, validated through pressure distribution maps. This novel, non-invasive technique offers precise, reliable, and scalable solutions for hydrogen leak detection, making it suitable for dynamic operational environments and industrial applications. The findings significantly advance hydrogen’s safety diagnostics, supporting the broader adoption of hydrogen-based energy systems.