This paper presents a novel numerical model, based on the Finite Element (FE) method, for the simulation of a welding process aimed to make a two-passes V-groove butt joint. Specifically, a particular attention has been paid on the prediction of the residual stresses and distortions caused by the welding process. At this purpose, an elasto-plastic temperature dependent material model and the “element birth and death” technique, for the simulation of the weld filler supply over the time, have been considered within this paper. The main advancement with respect to the State of the Art herein proposed concerns the development of a modelling technique able to simulate the plates interaction during the welding operation when an only plate is modelled, taking advantage of the symmetry of the joint; this phenomenon is usually neglected in such type of prediction models because of their complexity. Problems arising in the development of this modelling technique have been widely described and solved herein: transient thermal field generated by the welding process introduces several deformations inside the plates, leading to their interaction, never faced in literature. Moreover, the heat amount is supplied to the finite elements as volumetric generation of the internal energy, allowing overcoming the time-consuming calibration phase needed to use the Goldak’s model, commonly adopted in literature. The proposed FE modelling technique has been established against an experimental test, with regard to the temperatures field and to the joint distortion. Predicted results showed a good agreement with experimental ones. Finally, the residual stresses distribution in the joint has been evaluated.