Developing advanced electrocatalysts with low cost for electrocatalytic water splitting are highly desirable. Herein, we report the design of two-dimension on two-dimension growth of hierarchical Ni_0.2Mo_0.8N nanosheets on Fe-doped Ni₃N nanosheets supported on Ni foam (Ni_0.2Mo_0.8N/Fe–Ni₃N/NF) via hydrothermal reaction and nitridation treatment. In the hierarchical structures, small Ni_0.2Mo_0.8N nanosheets were uniformly anchored on Fe–Ni₃N nanosheets. Due to enhanced electron transfer between Ni_0.2Mo_0.8N and Fe–Ni₃N, Ni_0.2Mo_0.8N/Fe–Ni₃N/NF exhibits superior electrocatalytic activity for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). After stability tests for 50 h, Ni_0.2Mo_0.8N/Fe–Ni₃N/NF exhibits negligible degradation of the current density for the OER (91% remain) and HER (95% remain), suggesting excellent stability. Owing to the outstanding performance, Ni_0.2Mo_0.8N/Fe–Ni₃N/NF display a cell voltage of 1.54 V (10 mA cm⁻²) for electrocatalytic overall water splitting.