Passive radiative cooling is emerging as a sustainable strategy to reduce energy consumption by emitting heat directly through Earth’s atmospheric transparency window. Here, we demonstrate transparent wood-based biocomposite coatings as an eco-friendly solution for passive radiative cooling under direct sunlight. We fabricated freestanding, micron-thick coatings using wood scaffolds functionalized with ZnO nanoparticles, followed by thiol–ene in situ polymerization to improve transparency and mechanical resilience. These coatings exhibit high visible transparency combined with exceptionally strong mid-infrared emissivity (∼0.95). When applied onto silicon substrates exposed to direct sunlight, ZnO-functionalized coatings effectively lowered the substrate temperature by ∼6–7 °C. This was primarily attributed to enhanced thermal radiation, highlighting their potential for mitigating overheating in solar cells and other sunlight-exposed structures. Additionally, the enhanced mechanical properties of these biocomposites provide versatility for structural and optical applications, positioning them as a cost-effective, bio-based alternative to traditional cooling technologies.