This study investigates the combined effects of multi-walled carbon nanotubes (MWCNT) and silica fume on the workability, microstructure, thermal stability, and compressive strength of concrete. The addition of these admixtures slightly reduced slump performance due to their reinforcing effect. However, the concrete remained within the medium workability range. Scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) confirmed the successful integration of MWCNT and silica fume. The analysis revealed improved matrix densification and stronger interfacial bonding. Thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy provided further insights into the material’s thermal stability and chemical interactions. These microstructural and thermal improvements contributed to a 31.5% increase in compressive strength compared to the control mix. The findings highlight the synergistic role of MWCNT and silica fume in enhancing concrete performance.