The new 2,3-diphenylquinoxalin-6-amine (dpqa) was designed and synthesized through an efficient and high yield condensation process. Data from FTIR and 1 H-NMR spectroscopy have been adopted to ascertain the molecular structure of benzoxazine compounds. Furthermore, the quinoxaline amine based benzoxazine (BA–dpqa) was synthesized using bisphenol-A and paraformaldehyde followed by combining different weight percentages (1, 5 and 10 wt%) of (3-glycidyloxypropyl)trimethoxysilane functionalized CNT–PbS with benzoxazine to obtain nanocomposites. The thermal and morphological properties of the quinoxaline amine based neat polybenzoxazine matrix poly(BA–dpqa) and CNT–PbS/poly(BA–dpqa) composites were analysed by XRD, TGA and SEM analysis. The values of the degradation temperature ( T d ) obtained for neat poly(BA–dpqa) and 10 wt% CNT–PbS/poly(BA–dpqa) composites are 414 °C and 424 °C. Furthermore, the chair yield percentage was calculated as 33% and 35% respectively. The water contact angle of polybenzoxazine gradually increased from 89° to 127° proportional to the content of CNT–PbS. Among the composites, 10 wt% CNT–PbS reinforced poly(BA–dpqa) nanocomposites possess higher dielectric constant ( k = 11.0) than other composites. The pseudocapacitor nature of the prepared electrodes is demonstrated by the good electrochemical performance according to the CV curve. Also, the prepared 10 wt% CNT–PbS/poly(BA–dpqa) (637 F g −1 at 5 A g −1 and 11.8 Ω) electrode shows better capacitance and lower charge transfer resistance values than 5 wt% CNT–PbS/poly(BA–dpqa) (613 F g −1 at 5 A g −1 and 13.2 Ω) and neat poly(BA–dpqa) (105 F g −1 at 5 A g −1 and 15.6 Ω) according to the charge/discharge curves and EIS spectra. 10 wt% CNT–PbS/poly(BA–dpqa) shows 99.2% cycling efficiency even at the 2000th cycle, which indicates the good electrochemical performance of the prepared electrode.