Today, wire arc additive manufacturing (WAAM) can be used to fabricate critical structural steel components. It allows to fabricate highly optimized shapes achieving very high levels of material’s capacity utilization. But there are certain scientific challenges linked to this manufacturing technique that need to be explored and the fatigue resistance of WAAM components is one of them. Welding parameters influence the final geometry, microstructure, residual stress state and mechanical properties of workpieces made by WAAM and studying them all through tests is impractical. Finite Element models play a key role in resolving these issues. In this research, the behaviour of wire arc additively manufactured carbon steel elements is investigated numerically and experimentally. The sample was manufactured by cold metal transfer (CMT) welding process using the grade 3Dprint AM 35 (S355) following a welding procedure optimised to limit the welding-induced imperfections. A series of microstructural and mechanical investigations were carried out including: (i) hardness tests, (ii) static tensile tests, and (iii) cyclic fatigue tests. Temperature and strain fields were measured during the fabrication of the samples. A Finite Element (FE) model using a moving heat source (user subroutine) was built in Abaqus to simulate the material deposition. The obtained numerical results were compared to the measurements, and it was shown that the stress and temperature fields could be reproduced accurately. The validated FE model was then used to theoretically predict the fatigue lives via linear elastic fracture mechanics (LEFM) and a good agreement was obtained between experimental and numerical results.