Thermoelectric (TE) materials can convert thermal energy into electrical energy through their Seebeck effects. As a green energy source, TE materials can recover waste heat from various heat sources. Polymer-based materials have recently attracted significant research interests to replace semiconductors for TE applications due to many advantages of polymers over their semiconducting counterparts. The main challenge to develop polymeric TE materials is to enhance their energy conversion efficiencies by tuning the highly interrelated TE parameters (i.e., thermal conductivity, electrical conductivity, Seebeck coefficient). In the current study, poly(vinyl alcohol) (PVA)/polypyrrole (Ppy) nanocomposite foam samples were fabricated, with enhanced TE efficiencies, using freeze-drying and vapor-phase oxidative polymerization techniques. An aqueous PVA/iron (III) chloride solution was prepared and freeze-dried to create a foam sample with high porosity and open-cellular structure. The PVA/oxidant foams were then exposed to pyrrole (py) monomer at room temperature to initiate polymerization. Graphene nanoplatelets (GnP) were also incorporated within the polymer matrix to promote the electrical conductivity and the Seebeck coefficients of the samples. The effects of oxidant concentration and GnP content on the TE properties of the nanocomposite samples were investigated in this research. Experimental results revealed that incorporating Ppy effectively enhanced the nanocomposite’s electrical conductivity, which was several orders of magnitude higher than the reported values for PVA/multi-walled carbon nanotubes nanocomposites. The addition of GnPs, on the other hand, significantly promoted the samples’ Seebeck coefficients. Moreover, introducing the foam structure helped to suppress the thermal conductivity of the samples. Consequently, the TE efficiency of the material system was significantly enhanced due to the partial decoupling of the three governing TE parameters.