Highly efficient electrocatalysts composed of earth‐abundant elements are desired for water‐splitting to produce clean and renewable chemical fuel. Herein, a heteroatomic‐doped multi‐phase Mo‐doped nickel phosphide/nickel sulfide (Mo‐NiPx/NiSy) nanowire electrocatalyst is designed by a successive phosphorization and sulfuration method for boosting overall water splitting (both oxygen and hydrogen evolution reactions (HER)) in alkaline solution. As expected, the Mo‐NiPx/NiSy electrode possesses low overpotentials both at low and high current densities in HER, while the Mo‐NiPx/NiSy heterostructure exhibits high active performance with ultra‐low overpotentials of 137, 182, and 250 mV at the current density of 10, 100, and 400 mA cm−2 in 1 m KOH solution, respectively, in oxygen evolution reaction. In particular, the as‐prepared Mo‐NiPx/NiSy electrodes exhibit remarkable full water splitting performance at both low and high current densities of 10, 100, and 400 mA cm−2 with 1.42, 1.70, and 2.36 V, respectively, which is comparable to commercial electrolysis. A heteroatomic‐doped multi‐phase Mo‐doped nickel phosphide/nickel sulfide (Mo‐NiPx/NiSy) electrocatalyst with abundant heterogeneous interfaces is designed and applied for robust full water splitting, which delivers 10 mA cm−2 at cell voltage of 1.42 V and 400 mA cm−2 at 2.36 V. Furthermore, the electrode exhibits high stability in overall water splitting without decay even after 50 h testing, which provides great potential for commercial applications.