Molybdenum sulfides have been identified as promising materials for catalyzing the hydrogen evolution reaction (HER) in acid, with active edge sites that exhibit some of the highest turnover frequencies among nonprecious-metal catalysts. The thiomolybdate [Mo3S13]2– nanocluster catalyst contains a structural motif that resembles the active site of MoS2 and has been reported to be among the most active forms of molybdenum sulfide. Herein, we improve the activity of the [Mo3S13]2– catalysts through catalyst–support interactions. We synthesize [Mo3S13]2– on gold, silver, glassy carbon, and copper supports to demonstrate the ability to tune the hydrogen binding energy of [Mo3S13]2– using catalyst–support electronic interactions and optimize HER activity.