The environmental friendliness of 3D printable mixes is most likely achievable through recycling industrial waste. The effect of partially replacing ordinary Portland cement (OPC) with different ratios (0%, 20%, 40%, and 60% by weight of OPC) of fly ash (FA) and ground granulated blast furnace slag (BFS) on various properties of 3D printable concretes has been studied. The water-to-binder ratio and aggregate volume percentage were 0.3 and 41%, respectively. A standard flow-table test was conducted to adjust superplasticizer dosages for the target flow diameter in the presence of a constant viscosity modifying agent content in all mixtures. A manual injection gun was used to simulate the printing process and monitor the buildability of the mixes. A rotational rheometer was employed to measure the rheological properties. Furthermore, ram extrusion and green strength tests were conducted to quantify the time-dependent properties at early ages. Flexural and compressive strengths were assessed at 7 and 28 days of standard curing. Finally, the embodied carbon (EC) and energy (EE) were evaluated. The findings of this study highlight that at an equal flow diameter, BFS and FA inclusion significantly influence extrusion forces, open time, and green strength of printable mixtures in contrasting ways. BFS improved the green strength, buildability, and static yield stress, increasing the green strength by up to 163.41%; however, it may reduce the open time proportionally with its content. In contrast, FA replacement can extend the open time by lowering the development of extrusion force. However, FA reduced the green strength, with a decline of up to 35.4%. Both pozzolans increased the 28-day flexural and compressive strength, but this effect was not observed in the 60% fly ash-bearing mixture. Overall, BFS outperforms FA in enhancing buildability and structural performance, particularly at an early age. Incorporating BFS and FA significantly reduced carbon emissions and embodied energy, with reductions of up to 40% and 41% for BFS and 62% and 57% for FA, respectively.