Single nonlinear optical crystals of L-Proline Potassium Bromide (LPPB) were synthesized and grown by dissolving L - proline and potassium bromide in 1:1 molar ratio using deionized water as the solvent. The crystal parameters of the grown crystals have been evaluated by single crystal and powder XRD methods. Optical spectral studies have been carried out to find the band gap and optical constants of the material. Second Harmonic Generation (SHG) study reveals the nonlinear optical (NLO) property of sample. Mechanical strength of the grown samples is tested by hardness studies. TG/DTA studies were carried out to confirm the thermal stability to the grown crystals. EDAX test was also carried out to test the presence of elements in the sample. The details of the method adopted for crystal growth and the results obtained through various characterizations are analyzed and interpreted in detail.