Selective laser sintering (SLS) is one of the most promising additive manufacturing technologies to produce functional end-use components using thermoplastic powders. This work proposes a design for selective laser sintering of multiwalled carbon nanotubes (MWCNTs) filled with polyamide 12 (PA12) polymer composites with enhanced thermophysical properties for aerospace and automotive applications. The MWCNTs were mechanically mixed with PA12 powder in 0.5 and 1.0 weight percentages to formulate the nanocomposite powders. The single layer samples of neat PA12 and new MWCNT-PA12 formulations were designed and fabricated using the SLS process. Thermogravimetry, Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, and Field Emission Scanning Microscopy were used to assess the thermophysical and physicochemical properties of the nanocomposites. The effect of laser processing parameters was experimentally evaluated for each composition for successful printing. The surface morphologies of the sintered samples were analyzed to determine the optimal processing parameters for the SLS processing of composite powders. The results showed that the addition of carbon nanofillers in the PA12 matrix has significantly affected the thermal and viscoelastic properties of the nanocomposites. The inclusion of MWCNTs has significantly increased the thermal degradation onset temperatures and hence widened the SLS processing window. The density of 0.5 wt% of MWCNT-PA12 printed samples was observed to be 10.5% higher, whereas the density of the samples printed with 1.0 wt% MWCNT-PA12 was 18.46% lower than the samples printed with neat PA12. Therefore, the 0.5% CNT-PA12 composition resulted in an optimal composition.