Photocatalytic splitting of water into hydrogen and oxygen by using visible light is considered to be a clean, green, and renewable route for solar energy conversion and storage. Although the Zn_1−xCd_xS catalysts show comparatively higher activity for photocatalytic hydrogen generation under visible‐light irradiation, they suffer from serious photocorrosion during the photocatalytic reaction. The deposition of a protective layer over the Zn_1−xCd_xS catalysts is believed to be an effective way to inhibit photocorrosion. However, only a few materials exhibit satisfactory catalytic properties for hydrogen evolution as well as a good protection ability. In this work, a new Zn_1−xCd_xS photocatalyst was developed for water splitting under visible‐light illumination by assembling an ultrathin NiO layer over Zn_0.8Cd_0.2S through an in situ photodeposition method. The as‐prepared NiO/Zn_0.8Cd_0.2S showed significantly higher activity for overall water splitting compared with Pt/Zn_0.8Cd_0.2S under the same conditions without photocorrosion. An apparent quantum efficiency of 0.66 % was achieved for hydrogen evolution at 430 nm with an accomplished multicycle stability for up to 12 h without any significant decay. The strong electronic coupling between the NiO layer and Zn_1−xCd_xS also promoted efficient charge separation and migration.