In this paper, a new volumetric heat source model is developed for predicting the weld bead geometry during plasma arc welding of thin sheets of titanium alloy. Numerical simulations are carried out with the proposed parabolic Gaussian heat source (PGHS) model and already prevailing familiar heat source models namely, conical heat source and modified conical heat source, using finite element package COMSOL. The temperature-dependent material properties for Ti–6Al–4V alloy are considered for performing numerical calculations, which tend to influence the temperature fields while computing. Besides, the effect of trailing gas shielding, latent heat, and radiative and convective heat transfer are taken into account while performing the transient thermal analysis which significantly alters the sensitivity and accuracy of the model. Experimental trials on thin titanium alloy sheets are carried out to enable the validation of the proposed PGHS model. Subsequently, the outcome reveals that the PGHS model is capable and proved its high degree of efficiency in predicting the weld bead geometry more accurately than the existing heat source models. The distribution of heat intensity along the thickness of thin sheet is observed to be parabolic as predicted by the proposed model. The prediction appears to have a good correlation with the experimental result and it is clearly perceptible that the parabolic shape is more reliable and yields greater accuracy of the proposed heat source model.