AbstractMXene‐transition metal dichalcogenide (TMD) heterostructures are synthesized through a one‐step heat treatment of Nb₂C and Nb₄C₃. These MXenes are used without delamination or any pre‐treatment. Heat treatments accomplish the sacrificial transformation of these MXenes into TMD (NbS₂) at 700 and 900 °C under H₂S. This work investigates, for the first time, the role of starting MXene phase in the derivative morphology. It is shown that while treatment of Nb₂C at 700 °C leads to the formation of pillar‐like structures on the parent MXene, Nb₄C₃ produces nano‐mosaic layered NbS₂. At 900 °C, both MXene phases, of the same transition metal, fully convert into nano‐mosaic layered NbS₂ preserving the parent MXene's layered morphology. When tested as electrodes for hydrogen evolution reaction, Nb₄C₃‐derived hybrids show better performance than Nb₂C derivatives. The Nb₄C₃‐derived heterostructure exhibits a low overpotential of 198 mV at 10 mA cm⁻² and a Tafel slope of 122 mV dec⁻¹, with good cycling stability in an acidic electrolyte.