The increasing energy demand and related environmental issues have drawn great attention worldwide, thus necessitating the development of sustainable technologies to preserve the ecosystems for future generations. Electrocatalysts for energy-conversion reactions such as the hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2RR) are at the heart of these renewable energy technologies, but they suffer from sluggish kinetics due to the multistep electron and mass transfer. State-of-the-art catalysts are thus highly desired to boost the conversion efficiencies, which are still inadequate. Recently, as a typical transition metal dichalcogenide, molybdenum disulfide (MoS2) with unique physicochemical properties has been verified as a promising material for catalyzing key electrochemical reactions (i.e., HER, NRR, and CO2RR), presenting excellent performances. Therefore, in this review, we give insight into the structure and synthetic strategies of MoS2. Recent advances in MoS2-based materials for the three key electrochemical reactions are briefly summarized. Open challenges and perspectives of MoS2-based electrocatalysts toward HER, NRR, and CO2RR are also outlined.