This study investigates the incorporation of natural soil (4% clay) as a supplementary fine aggregate in 3D concrete printing. The primary objective was to evaluate whether reducing binder content while increasing soil content could still yield printable mixes with adequate strength and enhanced carbon uptake. A blended binder comprising ordinary Portland cement (OPC), fly ash, and ground granulated blast furnace slag (GGBS) was used. Three mixes were designed: the control mix (C) with a sand-to-binder ratio of 1.6, and soil-based mixes A30 and A50 with ratios of 2.08 and 2.40, achieved by adding 30% and 50% of soil. Two curing regimes were applied: conventional water curing and accelerated carbonation curing (6 h CO2 exposure after 24 h of printing), followed by water curing. The experimental program examined fresh properties (extrudability and buildability), compressive strength development, and carbon uptake. Soil incorporation significantly improved fresh properties, allowing higher printable heights (435–446 mm) compared to the control (260 mm). However, soil-based mixes showed early-age strength reductions of up to 85%, though the gap narrowed up to 60% at 28 days due to continued hydration of the binder and the clay fraction. The overall reduction was obvious due to lower binder content. Carbonation further influenced strength development, causing up to 78% loss at 1 day but only up to 35% at 28 days, reflecting ongoing hydration and CaCO3 precipitation, which densified the system. The higher early-age losses were mainly linked to C–S–H decalcification. Despite reduced binder, soil-based mixes achieved 7–8% higher carbon uptake than the control. Overall, soil incorporation improved fresh properties and carbonation potential, while strength losses could be partially compensated through carbonation.