Electrochemical nitrogen reduction reaction (eNRR) at standard conditions shows promise as an innovative approach for artificial nitrogen fixation, potentially offering a more energy-efficient alternative to the Haber-Bosch method. Design and evolution of low-cost and high-efficiency electrocatalysts remain the significant challenge confronting eNRR. Single-atom catalysts have recently been intensively explored due to their 100% utilization, high activity, and high selectivity. Here, a series of transition metal atom anchored on biphenylene (TM−BPN, TM = Sc−Hg) are studied as electrocatalysts (SACs) for eNRR by density functional theory computation. Among them, 19 SACs are screened out as the most promising electrocatalyst with lower limiting potential than that on the stepped Ru (0001). The Re−BPN catalyst exhibits the highest catalytic activity with a lowest limiting potential of -0.48 V. In addition, the Re−BPN also exhibits high eNRR selectivity by suppressing the competing hydrogen evolution reaction with the Faradaic efficiency being ∼100%. Partial density of states and Bader charge analysis illuminate the origin of eNRR catalytic activity of TM−BPN. Furthermore, the SAC structure remains intact under 500 K with no bond breaking. This study deepens our insight into the utilization of SACs in N2 fixation, contributing significantly to the exploration of efficient electrocatalysts for eNRR.