<p>Being a major contributor to the global greenhouse gas emissions, the cement industry targets net-zero emissions by 2050 through lowering clinker CO₂ emissions via low-carbon raw materials and partial substitution of clinker with supplementary cementitious materials (SCMs). This study explores a sustainable approach to low-carbon cement through the dual integration of phosphogypsum (PG) and fly ash (FA) by-products as SCMs for potential CO₂ reduction. The synergistic effect of PG and FA on cement properties was investigated at different substitution rates of clinker.&#xa0;The results showed that the optimized mortar containing 10% purified PG and 10% FA exhibited remarkable mechanical properties, with compressive and flexural strengths of 57.8 MPa and 9.5 MPa, respectively, at 28 d. Notably, the optimized mortar composition outperformed the CEM II/B-M 32.5 mortar, with compressive and flexural strengths that are 41% and 16% higher, respectively. These findings highlight that the dual valorization of PG and FA not only enhances engineering performance but also presents a viable strategy for reducing CO₂ emissions in the cement industry by nearly 16% annually. This approach contributes to circular economic initiatives and offers significant environmental benefits. Furthermore, large-scale feasibility, PG treatment costs, and long-term durability should be further investigated.</p> Graphical abstract <p></p>