Electrochemical proton reduction is a promising energy storage method because H₂ molecule has a simple structure with a relatively low potential energy. Current interest in hydrogen catalysts has increased research efforts on synthetic analogs of hydrogenase active sites. In this study, we demonstrated the electrochemical H₂ evolution reactivity of [NNN^R‐Co(CH₃CN)₃]²⁺ (R  CH₂ (1b), NCH₃ (2b)) complexes and examined a proton‐relay process in the H₂ evolution reaction (HER). Upon one‐electron reduction, the Co(II) ion center in a high‐spin state dissociated a CH₃CN ligand, while opening a reaction site. Cyclic voltammograms of the Co complexes indicated quasi‐reversible Co(II/I) redox behaviors, and both complexes 1b and 2b showed catalytic H₂ evolution activity. Interestingly, 2b, assisted by a proton‐relaying NCH₃ group, exhibited more efficient catalytic activity than 1b.