This paper describes the 3D-printed open Double Square Loop (DSL) Frequency Selective Surfaces (FSSs) based Radio Frequency energy harvester specifically designed for the purpose of capturing Wi-Fi ambient RF energy. The proposed dual-band energy harvesting circuit is a suitable applicant for low-power green IoT Wireless Sensor Networks. The inclusion of FSS in the receiver improved the antenna’s gain by 42% and 74% at 2.4 GHz and 5.2 GHz, respectively, and consequently, enhanced the conversion efficiency. Due to FSS-backed dual-band antenna, the proposed configuration gathers a significant amount of RF ambient energy from the surroundings. The collected RF energy is then converted into DC voltage using a three-stage Villard RF rectifier cum multiplier. The Fused Deposition Modeling (FDM) of 3D printing is employed to create the designed prototype on a biodegradable Polylactic Acid substrate. RF measurements are taken with horn antenna and signal generator to evaluate the proposed design. At 2.4 GHz, the constructed prototype has a conversion efficiency of 67.90% and a corresponding output voltage of 2.36 V, whereas, at 5.2 GHz, it achieves an efficiency of 34.01% with output voltage of 1.67 V, at 0 dBm input power. The proposed configuration has a good correlation between simulated and measured outcomes.