It has been reported that partial substitution of cement with pre-hydrated cement kiln dust, known as cement waste-derived portlandite (CDP), combined with CO2 curing, can help in the reduction of carbon footprint and enhance certain engineering characteristics. This study explores the combined effects of controlled dehydration (DH) and carbonation curing (CC) on CO2 uptake and compressive strength of cement mortars incorporating CDP. CDP was used to replace cement from 0-40%, whereas dehydration (0, 1, and 2 h) and CC (0, 24, and 48 h) durations at 500 kPa were considered. CO2 uptake was strongly influenced by CDP content and DH–CC combinations, with cement-based uptake generally increasing as CDP content increased. For 24 h CC, 2 h DH produced comparable or improved uptake, while for 48 h CC, 1 h DH was more effective. Compressive strength decreased with increasing CDP content; however, up to 10% replacement showed no significant reduction. Strength improved with increasing DH and CC durations, although excessive carbonation duration was generally detrimental. A clear positive relationship between CO2 uptake and compressive strength was observed. The optimal balance between CO2 sequestration and mechanical performance was achieved at 20–30% CDP under 2 h DH and 24 h CC, corresponding to CO2 uptake of 7–11.7% by cement mass and compressive strength of 37.1 MPa (20%)–41.9 MPa (30%). These findings demonstrate that the DH–CC approach is an effective strategy for developing sustainable and low-carbon cementitious materials.