Cement production poses a considerable ecosystem threat due to carbonate decomposition in our environment. The substitution of cement with locally produced supplementary cementitious materials (SCMs) is currently one of the attractive and viable solutions. The objective of this investigation is, therefore, to assess the mechanical and durability performance of silica fume, eggshell powder, and their combination as partial replacements for cement in concrete. Furthermore, it examines the fresh and hardened properties of ternary and quaternary blended concrete incorporating SCMs including silica fume (SF), ground-granulated blast furnace slag (GGBS), and fishbone powder (FBP), along with microstructural analysis. The study is carried out in two series: Series 1 concentrates on binary and ternary blended cement, while Series 2 explores ternary and quaternary blended cement with a significant replacement of cement. In Series 1, the 15% replacement of cement with a mixture of silica fume and eggshell powder leads to a maximal improvement of 17.8% in compressive strength (to 46.4 MPa), 17.8% in splitting tensile strength, and 10.4% in flexural strength. Moreover, the water absorption rate decreases by 16.3% compared to the control specimen. The improved strength and durability are characterised by the additional formation of C-S-H gel through the reaction of silica fume and eggshell powder with cement. In Series 2, the quaternary mix containing SF, GGBS, and FBP outperforms that of ternary in strength (53.6 MPa compressive strength) and durability. Additionally, blended concrete with nano-silica fume (nSF) demonstrates superior performance to microsilica fume (mSF), owing to the chemical and filler effects of the SCMs. Microstructural analysis reveals that the optimal quaternary blended concrete, consisting of 10% nSF, 20% GGBS, and 2.5% FBP, exhibiting a denser morphology, particularly in the interfacial transition zone, indicating a high concentration of hydrates.