Conductive polyetherimide (PEI) based filaments can fulfil the gap between the design and manufacturing of functional and structural components through additive manufacturing, particularly in highly demanding applications such as electromagnetic interference (EMI) and radiofrequency (RF) shielding, thermal protection systems (TPS) in aero– space structures and also as capacitive touch sensors and conductive circuitry for designing human interface devices. In this study, we systematically described the fabrication of carbon nanotubes (CNTs) reinforced PEI filaments complemented by a custom–built extrusion process facilitating low weight fraction of nanomaterial addition. Neat PEI and CNTs reinforced PEI (CNTs/PEI) filaments at dierent CNTs weight fractions ranging from 0.1 to 7 wt. % were fabricated to enable the transfer of superior properties of CNTs into additive manufacturing polymer feedstock materials. Dierential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) traced CNTs in dierent thermally driven domains and noted that CNTs loadings up to 7 wt. % did not change kinetic thermal transitions. Morphological investigations by scanning electron microscope (SEM) and transmission electron microscope (TEM) showed eectively dispersed and distributed CNTs in PEI matrix even at high CNTs loadings. CNTs were aligned as a consequence of the successful extrusion process of PEI using high shear forces, and no trace of agglomerates was observed. The rheological percolation was found to be higher (0.25 wt. % CNTs/PEI) than electrical percolation (0.1 wt. % CNTs/PEI) since the system reached to an electrical percolation within the formation of a continuous conductive path at lower CNTs loadings. Rheological percolation network was not fully achieved till completion of intersected and homogenous CNTs network was completed. With the 7 wt. % CNTs loading, the highest electrical conductivity of CNTs/PEI filaments was reported as 2.57 10-1 S/cm. A 55% enhancement was also achieved when 5% wt. CNTs were introduced to PEI filament but in a trade–o in elongation at break c.a. 65 %.