A CdS–MoS₂ photoelectrode with a double-layer core–shell structure was prepared using a simple electrodeposition–in situ sulfurization method on a Mo substrate. The photocatalytic activity of as-prepared electrodes was evaluated using a photoelectrochemical H₂-generation experiment. The photocurrent and photon–electron conversion efficiency of the CdS–MoS₂ photoelectrode were nearly double those of a CdS photoanode prepared on FTO glass. The high activity of the CdS–MoS₂ photoelectrode was due to the higher separation efficiency of carriers caused by the formed CdS–MoS₂ Janus heterojunction structure, which made directional transmission and electron–hole separation possible. Our experiments show that, in addition to being a good co-catalyst in powder material for photocatalytic hydrogen production, MoS₂ can also be used as an electron acceptor layer to enhance electron–hole separation.