A large (∼20 mm diameter and 80 mm length) single crystal of L-arginine phosphate monohydrate (LAP) has been grown for the first time by the unidirectional Sankaranarayanan–Ramasamy method in an aqueous medium in a specially designed constant-temperature bath. The crystal structure has been confirmed by powder X-ray diffraction. The crystalline perfection was assessed by high-resolution X-ray diffractometry (HRXRD) which found that the quality of the grown single crystal is quite good. HRXRD studies along different directions show that the crystal contains a low density of edge-type dislocations formed along the growth direction. The thermal stability was assessed using thermogravimetric/differential thermal analysis. The mechanical behaviour was studied using an Omnitech micro-hardness tester. The dielectric studies were carried out over a wide frequency range of 10 Hz to 5 MHz at room temperature. The characterization studies reveal that the grown bulk single crystal of LAP is suitable for device applications.