Metal Additive Manufacturing (MAM) has emerged as an advanced manufacturing technology capable of producing complex geometries with high material utilization, design flexibility, and reduced manufacturing waste. The increasing industrial adoption of MAM in aerospace, automotive, biomedical, and energy sectors has accelerated research on process optimization, material performance, and defect mitigation. This review critically examines major metal additive manufacturing processes, including Powder Bed Fusion (PBF), Directed Energy Deposition (DED), Wire Arc Additive Manufacturing (WAAM), and Binder Jetting, with emphasis on their process mechanisms, material characteristics, and industrial applications. Despite substantial advancements in process development and industrial implementation, several technical challenges like residual stresses, porosity, cracking, anisotropy, distortion, and surface irregularities arise which are systematically discussed along with their formation mechanisms and mitigation strategies. This review critically examines major metal additive manufacturing processes with emphasis on residual stress development, defect formation mechanisms, material behaviour, and process–microstructure–property relationships. The review further discusses commonly used metallic materials including titanium alloys, stainless steels, aluminum alloys, nickel-based superalloys, cobalt-chromium alloys, and metal matrix composites. In addition, industrial applications, advantages, limitations, post-processing techniques, and defect mitigation strategies associated with metal additive manufacturing are comprehensively reviewed. Recent developments in intelligent manufacturing, in-situ monitoring, process optimization, and data-driven manufacturing approaches are also discussed to highlight future research opportunities and technological advancements in metal additive manufacturing.