High-strength concrete (HSC) is increasingly used in modern infrastructure due to its superior mechanical performance and durability. However, low water–binder ratios often reduce workability and affect durability. This study examines the influence of partial replacement of cement with silica fume and fly ash on the strength development and durability characteristics of high-strength concrete. M60 grade concrete was produced using Ordinary Portland Cement, with silica fume and fly ash added in equal proportions as supplementary cementitious materials. Cement replacement levels of 0%, 5%, 10%, 15%, and 20% were considered. Fresh concrete properties were evaluated using slump and compaction factor tests, while hardened concrete performance was assessed through compressive strength, flexural strength, split tensile strength, water absorption, sorptivity, and acid resistance tests. Results indicate that workability decreases with increasing replacement levels due to the high fineness of silica fume and fly ash. Mechanical strength properties improved significantly up to an optimum replacement level of 10%, beyond which strength reduced due to cement dilution. Durability tests showed a slight increase in water absorption and sorptivity at higher replacement levels, while acid resistance improved marginally at lower replacement levels. Overall, a combined replacement level of 10% silica fume and fly ash provides the best balance between strength enhancement and durability performance in high-strength concrete.