In this work, a new ink formulation based on the use of a fully bio-based thermosetting resin as a binder, cellulose powders as rheology modifiers, and carbon nanotubes as conductive fillers was developed, and its potential as a functional material for additive manufacturing by direct ink writing was demonstrated. Electrical and rheological characterization of the nanocomposite at increasing CNT and cellulose concentrations was conducted in order to determine the optimal processing conditions and the printability window for the system. In addition, the resulting nanocomposite was further carbonized to yield a carbon-carbon nanocomposite with a better electrical conductivity. The results of the present study open the possibility of either integrating conductive circuits in a 3D-printed structure, or the printing of a bulk semi-conductive complex structure using a low-cost DIW 3D printing technique and mostly cost-effective renewable raw materials.