Niobium diselenide (NbSe2) belongs to the class of transition metal dichalcogenides (TMDCs) and exhibits peculiar features such as charge density waves, superconductivity, and periodic crystal lattice distortion. The main focus of the article is the synthesis and characterisation of NbSe2 NPs utilising the wet chemical precursor solution route at room temperature, followed by in-depth x-ray diffraction (XRD) characterisation and analysis using the aforementioned techniques. The EDS result demonstrated that the NbSe2 NPs are devoid of impurities and close to stoichiometry. The sample has a crystalline hexagonal structure with the lattice constants a = b = 3.443Å, c = 12.576 Å, and α = β = 90°, γ = 120°, according to the XRD results. The work emphasises the need of comprehending how lattice strain and crystallite size affect physical attributes. x-ray peak broadening was used to study the epitaxial crystallisation of NbSe2 NPs. Various methods for determining crystallite size, such as the Williamson–Hall (W-H) method, Debye–Scherrer plots, uniform deformation model (UDM), uniform stress deformation model (USDM), uniform deformation energy density model (UDEDM), size strain plot (SSP) method, and Halder-Wagner (H-W) method, are employed to comprehensively analyse the nanoparticle characteristics, and additionally, high-resolution transmission electron microscopy (HRTEM) is employed to visualise the morphology and particle size distribution of the synthesised NbSe2 NPs. Physical parameters, including lattice stress, strain, and energy density, are also evaluated more precisely from the XRD pattern reflection peaks. The outcomes shed light on the interplay between crystallite size, lattice strain, and their effects on the material's properties and showed excellent intercorrelation of the average crystallite sizes as estimated by employing various methods.