Hydrogen is considered as an important clean energy carrier for the future, and electrocatalytic splitting of water is one of the most efficient technologies for hydrogen production. As a potential alternative to Pt-based catalysts in hydrogen evolution reaction (HER), two-dimensional (2D) molybdenum sulfide (MoS₂) nanomaterials have attracted enormous research interest, while the structure control for high-performance HER electrocatalysis remains a considerable challenge due to the lack of efficient preparation techniques. Herein, we reported a one-pot chemical method to directly synthesize 2D MoS₂ with controllable layers. Multiple-layer MoS₂ (ML-MoS₂), few-layer MoS₂ (FL-MoS₂) and single-layer MoS₂ coating on carbon nanotubes (SL-MoS₂-CNTs) can be efficiently prepared through the modulation of experimental conditions. The enhanced catalytic activity in HER is demonstrated by reducing the layer number of MoS₂ nanosheets. Remarkably, the optimized SL-MoS₂-CNTs sample showed long-term durability with an accelerated degradation experiment even after more than 10 000 recycles, and high HER activity with an onset overpotential of only ∼40 mV vs. RHE. This study introduces a novel, cheap and facile strategy to prepare layer-controlled 2D MoS₂ nanosheets in a large quantity, and is expected to broaden the already wide range energy applications of 2D MoS₂ nanosheets.