Neutron resonance spectroscopy is demonstrated as a viable and reliable method for the determination of sample temperatures in high-pressure, high-temperature neutron diffraction studies at neutron spallation sources. The technique operates by characterizing the thermally induced Doppler broadening of neutron absorption resonances of heavy nuclei present within the sample assembly observed in transmission. Accuracies of +/-10 K have been readily achieved with data acquisition times of approximately 40 min. It is shown that the temperatures determined by this technique are independent of the sample pressure provided that the sample temperature is kept above the Debye temperature of the material whose resonances are being examined. A short list of candidate resonances for temperature measurement by neutron resonance spectroscopy is presented and suggestions volunteered for the combinations of elements most suitable for temperature measurement based on the experience of the authors.