Hybrid composites are at the forefront of technological developments due to their high thermal conductivity and thermal stability requirements. Hybrid composites are complex to machining due to the hard reinforcement particles contained in them and may cause structural defects. For this reason, although they are at the forefront, they are not preferred much in the manufacturing industry. This study was carried out to increase the machining efficiency of hybrid composites and, at the same time, to encourage the use of these composites in industry by reducing the environmental impact. In this study, the effects of different cooling/lubrication conditions on the surface roughness, tool wear, cutting temperature, and energy consumption of Cu–6Gr/SiC–WC hybrid composites by CNC milling were investigated. For this purpose, six material types (1–2–3–4–5–6), three cutting speeds (150–200–250 m/min), three feed rates (0.15–0.20–0.25 mm/rev), and three cooling/lubrication environment (dry-MQL-cryo-LN2) was selected. It was determined that the best option in terms of surface quality is the MQL environment. Cryo-LN2 environment reduces tool wear, cutting temperature, and energy consumption by 67%, 31%, and 14%, respectively, compared to the dry environment. Additionally, the wear mechanisms occurring on the cutting tool were examined by SEM/EDS analysis. In general, the cryo-LN2 strategy can be used as the best option for sustainable milling of hybrid composites. The results obtained are promising for using Cu–6Gr composites in the manufacturing industry, and these results are seen as innovations for the machinability results of hybrid composites.