A new organic-inorganic hybrid salt (CH6N3)2[Fe(C2O4)2(H2O)Cl] (1) (CH6N3+ = guanidinium cation) has been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction, EPR, SQUID magnetometry and Hirshfeld surface analysis. The asymmetric unit of salt 1 consists of one [Fe(C2O4)2(H2O)Cl]2– complex anion and two protonated guanidine molecules 2 CH6N3+. The FeIII ion in the complex anion shows a distorted octahedral coordination environment, with four O atoms from two chelating oxalate dianions, one O atom from a water molecule and one Cl− anion. A packing diagram of 1 highlights pillars of the [Fe(C2O4)2(H2O)Cl]2– complex anions and guanidinium CH6N3+ cations along the crystallographic a axis. These ionic entities are connected via intermolecular O–H···O, N–H···O and N–H···Cl hydrogen bonds into a three-dimensional network. Investigation of the thermal behavior of the compound confirmed its anhydrous character. The EPR spectrum of 1 corresponds to the Fe(III) oxidation state in an octahedral environment. The magnetic susceptibility measurements in the 2–300 K temperature range revealed weak antiferromagnetic interactions in salt 1. Hirshfeld surface analysis has also been evaluated to reveal various intermolecular interactions in 1.