Hydrogen zirconium phosphate (HZP) is a ceramic material with the formula HZr2(PO4)3 that can potentially offer anhydrous protonic conductivity, with thermostability for the intrinsic protons up to 650 ˚C, and good chemical stability in aqueous environments or acid gases. Despite the attraction of these features for electrolyte applications, such as gas separation, fuel cells or electrolysers, work on this material remains in its infancy. A possible reason for this lack of attention may be related to the complexity to obtain the HZP material as a pure phase. For this reason, the current article examines a new hydrothermal synthesis method to produce the ammonium precursor, NH4Zr2(PO4)3, in its phase pure form, and consequently a refined overall route to produce the desired HZP target material. In the synthesis of the ammonium precursor, we underscore the precise control of reaction conditions that are necessary to obtain the pure NH4Zr2(PO4)3 material, both in its cubic and hexagonal structural polymorphs. For reaction times of 10 hours, the cubic phase is obtained by employing a hydrothermal temperature of 150 °C and an aqueous ammonia volume of 2.1 mL, while the hexagonal phase is obtained for a hydrothermal temperature of 200 °C and an aqueous ammonia volume between 2.3 and 2.4 mL. Subsequently, we investigate the required conditions to convert hexagonal NH4Zr2(PO4)3 fully to hexagonal HZr2(PO4)3 via thermal treatment at 600 °C for 5 hours, assessed by a combination of X-ray diffraction and infrared spectroscopy.In this way this article aims to open up further research on this interesting HZP material by documenting a robust route for its preparation.