The ability of the polymer‐based graphitic carbon nitride (g‐C3N4) as a gas sensor toward NO, NO2, CO, CO2, SO2, SO3, and O2 gasses is assessed using density functional theory (DFT) calculations in terms of energetic and electronic transport characteristics. In particular, this study is aimed to explore the role of zigzag and armchair edges of the g‐C3N4 sheet on sensing performances. The electronic properties of adsorption systems, such as Bader charge analysis, band gaps, work function, and density of states (DOS), are used to understand the interaction between the adsorbed gas molecules and the g‐C3N4 sheet. Our calculated results indicate that SOx (SO3 and SO2) gasses have higher adsorption energies on the g‐C3N4 sheet than other gasses. Furthermore, the transport properties, such as current–voltage (I‐V) and resistance‐voltage (R‐V) curves along the zigzag and armchair directions are calculated using the non‐equilibrium Green's function (NEGF) method to understand the performance of the g‐C3N4 sheet as a prominent conductive/resistive sensor. The I‐V/R‐V results indicate that the zigzag g‐C3N4 sheet has excellent sensing ability toward SOx gasses at low applied voltages. However, the presence of H2O degrades the sensing performance of the armchair g‐C3N4 sheet. Theoretical recovery time has also been calculated to evaluate the reusability of g‐C3N4 sheet‐based gas sensors. Our results reveal that the zigzag g‐C3N4 sheet‐based sensing device has a remarkably high sensitivity (>300%) and selectivity toward SOx gasses and has the potential to work in a complex environment.