<p>Wire Arc Additive Manufacturing (WAAM) is prone to various defects arising from its inherent welding-based process, layer-by-layer fabrication, and the complex thermal-mechanical interactions involved. The main challenge in WAAM is managing these variables to produce parts with consistent and reliable properties. Despite employing optimal parameters such as cold metal transfer (CMT) power, wire feed speed, deposition speed, layer thickness, wire diameter, travel speed, and shielding gas flow rate to achieve a uniform temperature distribution during the printing process, some parts made with these technologies still experience defects. These include surface roughness, cracking, and porosity, which represent significant knowledge gaps in the field. This critical review aimed to identify the root causes of defect formation in the WAAM process. Defects like porosity, residual stresses, lack of fusion, spatter, inclusions, distortion, and cracking can negatively affect the surface quality and the mechanical and microstructural properties of WAAM-produced stainless steel if not adequately controlled. To address this gap, the paper thoroughly examines techniques for reducing defect formation, identifies the causes of these defects and mitigation approaches, and highlights the benefits of selecting suitable optimum process parameters to fabricate defect-free WAAM stainless steel components. One of the primary contributions of this review is the establishment of a framework for future researchers to control the sources of defect formation in the WAAM system, ultimately leading to the creation of defect-free metallic components.</p>