The reactivity and strength of geopolymers produced from low-calcium red mud (RM) are limited under non- carbonation curing. This study investigates the effects of steel slag (SS) incorporation and carbonation curing on an RM-SS geopolymer paste. Red mud was replaced with steel slag at 20,40,60,80 & 100%, activated using sodium hydroxide solutions (2M,4M,6M & 8M) and subjected to non-carbonation and CO2 curing. Compressive strength tests, XRD, and SEM analyses were performed to evaluate the effects. Steel slag incorporation enhances the compressive strength of non-carbonated geopolymers through C-S-H, N-A-S-H type and C-A-S-H type gel formation and matrix densification. CO2 curing reduced the strength owing to CaCO3 formation, although samples with optimal slag content maintained enhanced strength through microstructural densification. The Peak compressive strength occurred at 4M for both curing conditions, whereas lower and higher molarities showed poorer performance. XRD analysis revealed that increased SS content enhanced the amorphous hump 20°–38° and gel formation. Carbonated 4M samples maintained an amorphous structure, while low-molarity mixes showed significant gel carbonation. SEM observations showed dense matrices with well-developed gels in 4M non-carbonated samples and disrupted networks with post-carbonation carbonate deposits. The incorporation of steel slag with 4M activation enhances the strength and carbonation resistance of RM-based geopolymers, offering sustainable waste valorization.