The asymmetric unit of the title 1:1 salt 1,2,4-triazolium hydrogen oxalate, C2H4N3 +·C2HO4 − (I), comprises one 1,2,4-triazolium cation and one hydrogen oxalate anion. In the crystal, the hydrogen oxalate anions are linked by O—H...O hydrogen bonds into chains running parallel to [100]. In turn, the anionic chains are linked through the 1,2,4-triazolium cations by charge-assisted +N—H...O− hydrogen bonds into sheets aligned parallel to (01\overline{1}). The sheets are further stacked through π–π interactions between the 1,2,4-triazolium rings [centroid-to-centroid distance = 3.642 (3) Å, normal distance = 3.225 (3) Å, slippage 1.691 Å], resulting in the formation of a three-dimensional supramolecular network. Hirshfeld surface analysis of the title salt suggests that the most significant contributions to the crystal packing are by H...O/O...H and H...N/N...H contacts involving the hydrogen bonds.