The effects of blend ratio and MWCNT loading on the morphology, electrical properties and electromagnetic shielding performance of poly(trimethylene terephthalate) (PTT)/polypropylene (PP) blend nanocomposites were studied. To understate the state of dispersion of the MWCNTs, PTT/PP blend nanocomposites were systematically analyzed using scanning electron microscopy and high resolution transmission electron microscopy. Fourier transform spectroscopy (FT-IR) and Raman spectroscopy techniques were used to understand the chemical interactions between the blend components and fillers. Among the nanocomposites of all blend composition with 1 wt% MWCNTs, composites with high wt% PTT (90PTT/10PP/1MWCNT) showed better electrical properties due to the double percolation phenomenon. The shielding effectiveness (SE) was investigated in the S-band frequency range and 90PTT/10PP/1MWCNT showed a very good shielding effectiveness for electromagnetic radiation. Further studies with different MWCNT loadings showed that the 90PTT/10PP blend with 5 wt% MWCNTs indicated high dielectric properties and a maximum SE of ∼40 dB. The conductivity results were linearly fitted by a power law and the obtained percolation threshold was found to be around 0.5 wt% MWCNTs. Theoretical models were also applied for the DC conductivity data to explain the conductive mechanism in the polymer blend nanocomposites.