The construction sector faces huge pressure to adopt sustainable practices and reduce its environmental impact. This study explores the innovative use of mussel shells, a by-product of the seafood industry, silica fume and fly ash in cement mortar to enhance both sustainability and mechanical properties. Two important issues are addressed by the integration of these waste elements: efficient waste management and the creation of sustainable building materials. Mussel shells were processed by cleaning, oven dried at 60°C temperature for 24 h and grinded to achieve a suitable particle size for use as a partial replacement by weight of cement. Silica fume and fly ash, known for their pozzolanic properties, were used to partially replace sand. Various mix designs were prepared with different proportions of mussel shells (10%, 20%, 30%), silica fume (5%), and fly ash (5%). Mechanical tests, including compressive strength and flexural strength were conducted to evaluate the performance of the modified mortars after 7, 14 and 28 days. The results demonstrate that the combined use of mussel shells, silica fume, and fly ash significantly enhances the mechanical properties of cement mortar. Notably, the mix with 10% mussel shells, 5% silica fume, and 5% fly ash exhibited a remarkable increase in compressive and flexural strengths, achieving a 20% and 25% improvement, respectively, compared to the other mixes. In conclusion, the synergistic use of mussel shells, silica fume, and fly ash in cement mortar presents a promising approach to achieving sustainability and improved mechanical properties in construction materials. This research opens avenues for further exploration and optimization of alternative materials in the construction industry.