In this paper we investigated the spectral responsivity and photoresponse non-uniformity (PRNU) of a perimeter-gated single-photon avalanche diode (pg-SPAD) imager fabricated in a 0.35 µm complementary metal-oxide semiconductor (CMOS) process. Our experimental results show that perimeter gating reduces the imager's mean room temperature dark count rate (DCR) by two orders of magnitude and that it expands pixel spectral responsivity over the visible range. Further, our results show that the PRNU's dependence on noise is significantly reduced in high perimeter gate voltage regimes.