Abstract: In this study, the key process parameters for selective laser melting (SLM) and hot-pressing sintering (HPS) were systematically optimized using response surface methodology and orthogonal experimental design, respectively. The results indicate that the SLM process achieved a peak density of 88.67% at a laser power of 260 W, a scanning speed of 216 mm/s, and a scan spacing of 0.06 mm. Within the SLM process, both main and interaction effects were observed, with the order of influence being: laser power > scan spacing > scan speed. Conversely, the HPS process achieved a peak density of 94.92% at a sintering temperature of 805 °C, a holding time of 9 min, and a holding pressure of 50 MPa. Notably, the HPS process was governed solely by main effects—specifically sintering temperature>holding pressure>holding time—without significant interaction effects. Following optimization, the microstructure and properties of the composites fabricated via HPS were found to be superior to those produced via SLM. A comparative microstructural analysis revealed that while diamond particles in both composites avoided graphitization, the SLM-fabricated composite exhibited defects such as macropores and cracks, whereas the HPS-fabricated composite contained only minimal porosity. Furthermore, diamond particles in the SLM composites showed signs of fragmentation and debonding, whereas those in the HPS composites remained more intact, demonstrating superior morphological retention. This work provides valuable insights for the development of high-hardness copper-diamond composites using different processing routes.