The measurements of X-ray emission lines in atomic decay to the L-shell of thallium compounds were performed using a laboratory source-based conventional wavelength dispersive spectrometer. A large set of physical fundamental parameters such as X-ray transition energies, natural linewidths and relative transition probabilities were determined by robust spectral fitting trials. The current effort presents valuable intuition about the chemical effect in distinct thallium compounds, viz., pure Tl, TlX [X = (NO₃)₃, I, and Cl], and Tl₂X (X = O₃ and SO₄) on the L_p (p = l, α, η, β) X-ray lines. The investigation of chemical effects is one of the highly pressing tasks in understanding the various physical fundamental parameters in distinct metal-compounds. The results illustrate that the L_p (p = l, α, η, β) X-ray lines emitted from various thallium targets show energy shifts of ∼0.03–3.39 eV relative to the pure thallium target. In general, the outcomes of this study are consistent with the published data associated with the framework of the atomic Hartree–Fock (AHF), relativistic many-body problems in atoms and semi-empirical procedure developed within intermediate coupling calculations. For the first time, several physical fundamental parameters of thallium compounds have been investigated in this work, which are likely due to the adoption of robust spectral fitting procedures. The abruptly deviating peak profile variations found in distinct thallium-based metal-compounds can be reflected in the viewpoint of the linewidth, different electronegativity values of adjacent ligands, effective charge, changes in the transition probability, mixed oxidation states of thallium and valence to core exchange interactions. Furthermore, in the current study, the possible connection among X-ray line shifts and parameters are systematically scrutinised.