Mitigation of CO2 emissions has been a major societal concern in recent decades, and post-combustion capture of CO2 is an effective strategy proposed by the research community. Hierarchical porous geopolymer monoliths were fabricated using extrusion-based 3D printing for CO2 capture. The kaolin-based viscoelastic paste was first formulated using alkali activators and plasticizer, and it was observed that the viscosity increased over time. Second, the 3D printed porous monoliths were treated using different post-processing conditions like thermal curing, hydrothermal curing, and high-temperature thermal treatment and their physico-mechanical properties and CO2 adsorptive were investigated. Thermally cured and heated specimens exhibited an amorphous phase, while zeolite phases were observed in the hydrothermally treated specimens. Printed and subsequently hydrothermally treated mechanically stable specimens showed significantly higher CO2 adsorption (1.22 mmol/g) than conventionally casted geopolymer (0.66 mmol/g). Combining 3D printing with geopolymer technology could offer a sustainable approach design and structure adsorbents for CO2 capture.