Heteroatom and monometal decorated carbons (e.g., Fe-N/C or Co-N/C) are reported as effective oxygen reduction catalysts. However, they are seldom investigated for overall water splitting. Additionally, it is a significant challenge to increase the heteroatom content in carbon and achieve performance comparable or superior to precious metal-based catalysts. Here, NiFe-decorated, nitrogen, phosphorus, sulfur tri-doped nanocarbon with oxygen-containing groups, i.e., NiFe-N, P, S/C is reported as a highly-active electrocatalyst for overall water splitting. The carbons are prepared by one-step template-free pyrolysis. Alfalfa, one of the natural biomass with highest N: C ratio and significant P and S, works as the sole carbon and heteroatom source. During preparation, crucial factors including total amount of added transition metals, Ni to Fe molar ratio, and pyrolysis temperature, are optimized. Ni0.75Fe0.25-N, P, S/C prepared at 900 degrees C exhibits the best oxygen evolution reaction, hydrogen evolution reaction, and overall water splitting activity and stability. This material even exceeds the benchmark RuO2 in catalysing oxygen evolution reaction. Its overall water splitting activity is comparable to Pt/C-RuO2, making it one of the best water splitting electrocatalysts. This exciting performance is attributed to the high heteroatom level ((N + P + S + 0): C = 27.6 at.%), as well as the bimetal decoration.