Carbon materials are widely investigated for electromagnetic (EM) shielding and absorption. However, designing sustainable and tunable architectures that span multiple EM functions remains challenging. Here, we present a renewable materials strategy based on biopolymer-derived carbon nanofiber sheets where both carbonization temperature and fiber alignment are used to tune EM attenuation. The sheets were fabricated via high-speed electrospinning followed by carbonization at 600–1000 °C, enabling systematic tuning of microstructure, anisotropy, porosity, electrical conductivity and dielectric response. The electrospinning process produced aligned nanofiber networks that upon carbonization developed into anisotropic conductive pathways. Carbonization at 1000 °C yielded highly porous sheets with a specific surface area of 926 m2g−1 without external activation. The temperature-driven structural evolution resulted in a distinct functional transition: dielectric transparency at 600 °C, broadband absorption at 700–800 °C, and highly conductive reflective-dominating shielding at 1000 °C. The optimized sheet achieved shielding effectiveness of 54 dB at 18.3  GHz and 44.5 dB at 1.0 THz. Electrical anisotropy further enabled orientation-dependent shielding differences of 16.4 dB (GHz) and 21.8 dB (THz). These results establish aligned, renewable carbon nanofiber sheets as scalable platforms for next generation microwave and terahertz technologies.