<p>The effect of heat input and uniform temperature on the surface quality of wire arc additive manufacturing (WAAM) components is crucial for producing defect-free WAAM components. However, in most WAAM technologies, the heat input significantly impacts the layer-by-layer molten pool deposits, potentially leading to defect formation if not properly controlled and optimized. In this paper, we critically review the effect of heat input, uniform temperature distribution, interlayer temperature, and heat input parameters on the microstructure and mechanical properties of WAAM components during fabrication. Based on our findings, wire feed speed and torch speed parameters significantly control heat input in the WAAM process. It is established that optimizing parameters with a lower input can result in a finer and more homogeneous morphology, which can substantially enhance mechanical properties in the fabricated components. To manufacture high-quality metallic components that meet industrial demands, there is a need to provide an evidence-based framework for understanding these critical issues in the WAAM process, ensuring that WAAM processes are thoroughly planned before use in design and fabrication, which is one main contribution of this paper.</p>