This work reports a first-principles density functional theory (DFT) investigation of nitrobenzene (NB) sensing in pristine and metal-decorated biphenylene (p-BP and m-BP, m = Sc, Cu, Li, and Pd) 2D monolayer. Though the proposed p-BP monolayer displayed excellent adsorption of NB molecule compared to other reported 2D materials, it gets physisorbed on the p-BP surface with -0.621 eV adsorption energy. The metal decoration drastically reformed the NB adsorption capacity of BP and induced remarkable changes to the electronic properties. The ab-initio molecular dynamics simulations were employed to analyze the room temperature structural integrity of the m-BP-based NB sensor. Among all the systems considered, the Pd decorated BP monolayer came out as the potential NB sensor with a reasonable adsorption energy of -1.42 eV, charge transfer of 0.38 e, the recovery time of 0.92 s at 598 K, and structural solidity at ambient temperature. The higher diffusion barrier of 0.99 eV confirmed that the Pd dopant does not show the tendency to form clusters. The study demonstrates that the Pd decorated BP is highly apposite for NB sensing and is beneficial for practical application. Our study opens a new avenue for designing and developing efficient biomolecule sensors.