The substituted iron–thiolate complex [Fe2(μ-bdt)(CO)4{P(OMe)3}2] (bdt=benzenedithiolate) is an active catalyst for electrochemical hydrogen production in aqueous sodium dodecyl sulfate solution, with a high apparent rate constant of 4×106 M−1 s−1. The half-peak potential for catalysis of proton reduction is less negative than −0.6 V versus the standard hydrogen electrode at pH 3. Voltammetric data are consistent with the rate of electrode reaction controlled by diffusion. A mechanism that begins with the rapid protonation of the iron–thiolate catalyst is proposed. The Faradaic efficiency in diluted HCl solutions is close to 100 %, but the catalytic activity decayed after about twelve turnovers when electrolysis was carried out in the presence of acetic acid.