Taking advantage of carbonaceous composite materials in electrocatalysis or photocatalysis is a promising pathway for transforming biomass resources into sustainable energy-conversion systems. Herein, a carbonaceous composite catalyst based on the monodispersed silver vanadate nanoparticles (Ag3VO4 NPs) modification of biomass-derived porous carbon (named as AVO/PC) is proposed for ultrasensitive and electrochemical rapid detection of p-nitrophenol (p-NP) under acidic condition. The radish-derived three-dimensional porous carbonaceous aerogels as supporter subtly introduced in the carbonization process of alkaline activation remarkably promote the physicochemical properties of the biomass-derived porous carbon (PC), which can provide a favorable internal surface to load Ag3VO4 NPs. Subsequently, this electrochemical behavior of AVO/PC-modified glassy carbon electrode (AVO/PC/GCE) exhibits high sensitivity (4.95 mA mM−1 cm−2) and a varied linear detection range (1 μmol L−1 ≈ 1 mmol L−1), as well as reproducibility and stability for p-NP. Besides, the as-prepared AVO/PC demonstrates the enhanced photocatalytic degradation performance of rhodamine B (RhB), and the photocatalytic rate reaches to 94% in visible light irradiation. The findings should be useful for designing and constructing dual-purpose carbonaceous composite materials with potential applications in environmental monitoring and contaminant treatment.