In continuation to our previous work, the current investigation focuses on the effect of static applied pressure on the electrical and dielectric properties of multiwalled carbon nanotube (MWCNT)–polystyrene (PS)/2,3-hydroxy-2-naphthoic acid (β-HNA) nanocomposites. Additionally, optical properties of the nanocomposites are also investigated together with other further electrical, dielectric, and mechanical properties. Adding fixed amount of β-HNA (1.0 wt%) to MWCNTs enhances the MWCNT dispersion, reduces the percolation threshold to about 0.8 wt%, and increases the electrical conductivity up to eight orders of magnitude. The direct current (DC) and alternating current (AC) electrical properties of 1.0 wt% MWCNT–PS composites are investigated as a function of applied pressure. It is found that the current level increases while impedance values decrease with applied pressure during the cycle and the loading–unloading cycle has almost followed the same route indicating its reproducibility. Also the obtained results demonstrate that such a composite might act as pressure-sensitive conductive composite. Mechanical results show that the addition of MWCNTs (treated with β-HNA) to the neat PS increases the tensile strength and yield stress of the neat PS by about 12.39% and 12.53%, respectively, while the elastic modulus decreases by about 3.10%. However, further addition of MWCNTs decreases all mechanical parameters of prepared composites and these composites became more brittle. Besides, optical results indicate an enhancement in the neat polymer ultraviolet and visible absorption and a reduction in its optical energy gap (by about 14.1%) upon addition of 1.0 wt% MWCNTs (treated with β-HNA).