The photon response characterization of a Ø 25.4 mm 25.4 mm solution-grown stilbene based detector assembly was performed in the 59 keV–4.44 MeV energy range. Energy calibration was carried out using not only direct measurements but also via coincidence measurements in order to obtain more reliable results. Both methods gave consistent results. To establish an accurate model of the detector, its energy resolution was determined and included in MCNPX-PoliMi simulations. This model served to compute the gamma-response matrix in the 0.1–7.3 MeV energy range. This matrix was used as an input of the GRAVEL spectrum unfolding code when attempting to unfold the measured spectra of well-known sources. Despite a few discrepancies concerning peak intensities, the main gamma peaks were successfully identified in the 0.059–4.4 MeV energy range, thus confirming the utility of solution-grown stilbene as a low-resolution gamma spectrometer, especially for identifying the gamma component in neutron fields.