Both polymeric electrochromic and radar absorption materials have been considered as science hotspots over the past few decades. However, integrating both properties (electrochromic and radar absorption) in a single device has not been addressed to fabricate a multifunctional device so far. Thus, here, we endeavor to shed light on this uncharted area by presenting a new smart ternary nanocomposite (polythiophene-based/RGO-Fe3O4) which can provide both electrochromic and microwave absorbent features simultaneously. In this regard, we synthesized the binary Fe3O4-RGO nanocomposites with different contents of Fe3O4 nanoparticles. Then, this binary nanocomposite is utilized in combination with a polythiophene-based conductive polymer as a tricolor (RGB) organic electrochromic material to synthesize the smart ternary nanocomposite through both in-situ polymerization and physical mixing methods. The ternary nanocomposites containing different weight fractions of Fe3O4-RGO nanoparticles were used to assemble the rigid and flexible ECD devices using flat and fiber substrates such as glass-indium tin oxide (glass-ITO), polyethylene terephthalate-indium tin oxide (PET-ITO) and stainless steel wire (SSW). By applying a voltage of −2.1 to 2.1 v, a reversible color-switching ability was observed between green color (oxidized state), and red color (reduced state) for all ECDs. The average switching time and color memory for the SSW cell were determined to be about 3 s and 155 min, and for both glass-ITO and PET-ITO cells to be 2 s and 210 min, respectively. Additionally, the microwave absorption properties of the prepared ternary nanocomposites were characterized by measuring the electromagnetic parameters such as permittivity, permeability, and reflection loss. A ternary nanocomposite with 3 mm thickness filled with 50 wt% Fe3O4-RGO exhibited a maximum reflection loss as high as −30.2 dB (92% absorption) at 12.3 GHz (in the range of x-bond) with 1.1 GHz bandwidth.