Electrocatalytic water splitting for hydrogen production is an important pathway for achieving sustainable green hydrogen production. However, the shortage of freshwater resources limits its large-scale application, making it urgent to develop efficient and stable catalysts suitable for complex water sources, such as seawater and wastewater. In this study, a FeRu bimetallic nanocatalyst (Fe-Ru composite nanoparticles anchored on engineered biomass-derived carbon (FeRu-ERBC)) was constructed through biomass-derived two-dimensional porous carbon supports. It demonstrated excellent hydrogen evolution performance in alkaline, seawater, and chemical wastewater environments: with an overpotential of only 22.7 mV (10 mA·cm⁻²) in 1.0 M KOH and over 120 h of operational stability. Structural characterization and mechanistic studies, complemented by density functional theory (DFT) calculations, revealed that the support not only provides a high specific surface area and mass transport channels but also promotes atomic-level replacement of Fe by Ru, forming a tightly coupled Fe–Ru interface. X-ray photoelectron spectroscopy and in situ spectroscopy confirmed the electronic transfer from Fe to Ru at the interface, forming a “Fe^δ+–Ru^δ−” synergistic active center. This structure induced the regulation of the surface interfacial water network, thereby enhancing the overall reaction kinetics. This work provides a new strategy for the design of Ru-based catalysts with interface electronic regulation for real-world water environments and highlights the crucial role of biomass carbon supports in advancing green hydrogen technology.