Spray pyrolysis was used to prepare films of AgInS2 (AIS) with and without Sn as an extrinsic dopant. The photoelectrochemical performance of these films was evaluated after annealing under a N2 or S atmosphere with different amounts of the Sn dopant. DFT was used to calculate the band structure of AIS and understand the role of Sn doping in the observed properties. All AIS films were n-type, and Sn was found to increase the photocurrent and carrier concentration of AIS with an optimum doping level of x=[Sn]/([Ag]+[In])=0.02, which gave a photocurrent of 4.85 mA cm−2. Above this level, the Sn dopants were detrimental to the photoelectrochemical performance, likely a result of a self-compensating effect and the introduction of a deep acceptor level, which could act as a recombination site for photogenerated carriers.