The integration of 3D printing into the construction sector demands the development of tailored materials with optimized fresh and mechanical properties. The use of fiber-reinforced composites, however, imposes some challenges, as higher fiber content can lead to clogging in the pumping system, compromising extrudability. This study evaluates the effect of cellulose microfibers on fresh properties and printability of cement-based composites for 3D printing applications. Three volumetric fractions (2.5%, 7.5%, and 12.5%) of Cellulose microfibers were considered. Flow table, slump and drop-weight cone penetration tests were used to measure rheological properties. The extrudability of the mixtures was assessed using extrusion test, while printability and buildability were evaluated with a 3D robotic printer. The results demonstrated that cellulose microfibers significantly increase initial shear yield stress and thixotropy of the composites, improving mixtures’ cohesiveness during the printing process, enhancing the performance of 3D printable cementitious composites for construction. However, fibers volume fraction can be a limiting factor, as higher amounts can increase extrusion pressure.