Recycled tire rubber is an environmentally and economically beneficial material. Ground tire rubber (GTR) as a filler in a polymer matrix was used as an ink material (composite material) for material extrusion in a 3D printing process. The maximum allowable amount of GTR incorporated into the mixture without significantly altering the rheological behavior of the ink was set. Printability investigations revealed that pressure and speed show linear and power relationships, respectively, to the line width for three different amounts of GTR. Moreover, the post-curing time of 30 min at 115 °C was set as the full-cure condition to achieve polymerization of 80% or more for the 3D printed parts. Unidirectional tensile testing demonstrated that 3D printed specimens exhibit no degradation in tensile strength when compared to molded specimens. Moreover, printability and mechanical properties of functionalized GTR were investigated to determine if this material exhibits enhanced mechanical strength. Unidirectional tensile tests show that the maximum tensile strength for specimens with functionalized GTR was 20% higher than in specimens with non-functionalized GTR. In conclusion, 3D printing of GTR composites shows promise for using recycled GTR to create 3D structures with rubber-like properties.