A new application of in-fibre Bragg grating (FBG) sensors for the distributed measurement of temperature inside a polymer electrolyte membrane fuel cell is demonstrated. Four FBGs were installed on the lands between the flow channels in the cathode collector plate of a single test cell, evenly spaced from inlet to outlet. In situ calibration of the FBG sensors against a co-located micro-thermocouple shows a linear, non-hysteretic response, with sensitivities in good agreement with the expected value. A relative error of less than 0.2°C over the operating range of the test cell (~20–80°C) was achieved, offering sufficient resolution to measure small gradients between sensors. While operating the fuel cell at higher current densities under co-flow conditions, gradients of more than 1°C were measured between the inlet and outlet sensors. Due to their small thermal mass, the sensors also exhibit good temporal response to dynamic loading when compared with the thermocouple. Design and instrumentation of the graphite collector plate features minimal intrusion by the sensors and easy adaptation of the techniques to bipolar plates for stack implementation.