A review by a joint research team from the University of Toronto systematically outlines four unique microstructure and composition engineering pathways for producing high-performance metallic materials via Directed Energy Deposition (DED): (i) discontinuous functionally graded materials; (ii) continuous functionally graded materials; (iii) high-throughput in-situ alloying for new alloy design; and (iv) external field-assisted DED for controlling microstructure and composition. The study highlights material design strategies that are difficult or impossible to achieve with traditional manufacturing, analyzes the mechanisms of mechanical and multifunctional properties (thermal, magnetic, data encoding) from a process-structure-property relationship perspective, and discusses challenges in achieving target performance, providing a systematic reference for the next generation of high-performance metallic materials produced via DED.