The study of hydrogen bonds near symmetrisation limit at high pressures is of importance to understand proton dynamics in complex bio-geological processes. We report here the evidence of hydrogen bond symmetrization in the simplest amino acid−carboxylic acid complex, glycinium oxalate, at moderate pressures of 8 GPa using in-situ infrared and Raman spectroscopic investigations combined with firstprinciples simulations. The dynamic proton sharing between semioxalate units results in covalent-like infinite oxalate chains. At pressures above 12 GPa, the glycine units systematically reorient with pressure to form hydrogen-bonded supramolecular assemblies held together by these chains.