Bulk single crystals of diguanidinium phosphate monohydrate (G2HP) with dimensions up to 55 × 28 × 27 mm³ have been grown by solution growth methods. Thermal properties including specific heat, thermal conductivity and thermal expansion were investigated as a function of temperature. The specific heat was measured to be 1.339 to 1.614 J g⁻¹ K⁻¹ over the temperature range of 293 to 347 K. The thermal conductivities are descending as the temperature increases. The average linear thermal expansion coefficients along a and c axes from 298 to 338 K are α₁₁ = 1.878 × 10⁻⁵ K⁻¹ and α₃₃ = 1.930 × 10⁻⁵ K⁻¹, respectively. The laser-induced damage threshold measurements show that the G2HP crystal possesses an excellent resistance to laser radiation with a high threshold up to 5.29 GW cm⁻². The optical behaviors, including the transmission spectrum and reflective indexes, were investigated to study its linear and nonlinear optical properties. The results reveal that the crystal is a phase matchable nonlinear optical material in the visible and UV regions. A complete set of dielectric, elastic and piezoelectric constants of G2HP have also been measured, and the results display that the crystal also possesses fine piezoelectric properties with d₁₄ = 10.00. Furthermore, the structure–property relationships are discussed on the basis of the crystal structure combined with theoretical calculations. As a multi-functional crystal, G2HP is a particularly promising candidate for a variety of potential applications in many fields.