Two-dimensional (2D) superconducting systems have recently emerged as a frontier in condensed matter physics, driven by their unique physical properties and potential applications. Using first-principles calculations, we show that monolayer ZrX₂ (X = Cl, Br, I), which is a family of 2D semiconducting electrides, hosts phonon-mediated superconductivity under both electron and hole dopings. Electron doping in ZrX₂ can achieve high superconducting transition temperatures at very low concentrations, with ZrBr₂ reaching T_c = 30.0 K at 0.01 e/f.u., followed by ZrCl₂ (22.5 K at 0.05 e/f.u.) and ZrI₂ (18.1 K at 0.01 e/f.u.), for which the high T_c originates from the flat conduction band minimum, with Van Hove singularities nearby enhancing the density of states. In contrast, hole doping requires higher concentrations (0.2–0.25 h/f.u.) to activate superconductivity, yielding T_c ∼ 2 K, and approaches a magnetic instability at elevated doping levels. By comparing with InSe and LaBr₂, we identify the spatial location and orbital character of excess electrons as key factors determining the strength of hole-doped superconductivity and the nature of competing orders. These findings establish monolayer ZrX₂ as a platform for bipolar superconductivity in a 2D electride and provide insights into flat-band engineering for high-T_c superconductors.