Water electrolysis using non-precious transition metal-based electrocatalysts is one of the most promising ways for renewable hydrogen energy. Herein, we develop high-performance catalysts of trimetallic sulfide (Ni3S2-FeS-CoS) nanosheets decorated with bimetallic-nitroxide (NiCo(N,O)x) nanodots on a 3D NiFeCo foam by in situ fabrication with approaches of the dielectric barrier discharge (DBD) plasma and hydrothermal sulphurization. The resulting catalyst shows excellent electrocatalytic activity for overall water splitting in alkaline medium, with the overpotentials 82 m V for hydrogen evolution reaction (HER) and 170 m V for oxygen evolution reaction (OER) at a current density of 10 mA cm−2 (j10), which are very competitive to most recent non-noble-metal electrocatalysts. Specially, the nanodots help achieve ultra-stable electrocatalytic performance evidenced by negligible changes for the physico-chemical structure of catalyst after a harsh HER or OER test over 50 h. Our results offer a versatile approach for the development of next-generation electrocatalysts for hydrogen economy and other applications.