Combustion of rice husk produces a supplementary cementing material known as rice husk ash (RHA). Current studies on enhancement of physical properties and durability of cementitious composites with RHA are limited to applications in conventional construction. Automation in construction using additive manufacturing technique—commonly known as construction three-dimensional (3D) printing—is an emergent strategy. Because the printing process is formwork-free and requires a continuous deposition of layers with structural stability, mix design of a 3D printable concrete is different from conventional concrete. Portland cement replacement by RHA improves the sustainability of a mixture as a construction material. In this work, 20% by weight of cement is replaced with RHA. Compressive strength and workability loss of designed mixes—with and without RHA—were studied at early age and compared with fresh properties of proven printable mortar available in market. Incorporation of RHA has shown significant improvement in rheology of mortar at the rate required for construction 3D printing at large scale.