A combination of high dielectric permittivity (ε') and low dielectric loss (tan δ) is required for charge storage applications. In percolative systems such as conductive polymer composites, however, obtaining high ε' and low tan δ is very challenging due to the sharp insulation-conduction transition near the threshold region. Due to the particular arrangement of conductive fillers induced by both foaming and injection molding processes, they may address this issue. Therefore, this work evaluated the application of foam injection molding process in fabricating polymer nanocomposites for energy storage. Polypropylene-multiwalled carbon nanotubes (PP-MWCNT) composites were prepared by melt mixing and foamed using supercritical nitrogen (N2) in an injection molding process. Electrical conductivity (σ), ε' and tan δ of the samples were then measured. Also, scanning and transmission electron microscopy (SEM and TEM) was used to investigate the carbon nanotube’s arrangement as well as cellular morphology. The results showed that foam injection-molded composites exhibited highly superior dielectric properties to those of solid counterparts. For instance, foamed samples had ε'=68.3 and tan δ =0.05 (at 1.25 vol.% MWCNT), as opposed to ε'=17.8 and tan δ=0.04 in solid samples (at 2.56 vol.% MWCNT). Furthermore, the effects of various material and processing parameters such as MWCNT content, degree of void fraction, gas content, injection flow rate, and melt temperature on σ, ε' and tan δ of the foam injection-molded nanocomposites were investigated and optimum processing conditions were identified. The results of this work reveal that high performance dielectric nanocomposites can be developed using foam injection molding technologies for charge storage applications.