Development of earth-abundant electrocatalysts, particularly for high-efficiency hydrogen evolution reaction (HER) under benign conditions, is highly desired, but still remains a serious challenge. Herein, we report a high-performance amorphous CoMoS₄ nanosheet array on carbon cloth (CoMoS₄ NS/CC), prepared by hydrothermal treatment of a Co(OH)F nanosheet array on a carbon cloth (Co(OH)F NS/CC) in (NH₄)₂MoS₄ solution. As a three-dimensional HER electrode, CoMoS₄ NS/CC exhibits remarkable activity in 1.0 M phosphate buffer saline (pH 7), only requiring an overpotential of 183 mV to drive a geometrical current density of 10 mA·cm^–2. This overpotential is 140 mV lower than that for Co(OH)F NS/CC. Notably, this electrode also shows outstanding electrochemical durability and nearly 100% Faradaic efficiency. Density functional theory calculations suggest that CoMoS₄ has a more favorable hydrogen adsorption free energy than Co(OH)F.