Cellulose-based aerogels (CBAs), characterized by ultrahigh porosity (>90%), ultralow density (0.01–0.05 g·cm−3), and tunable functionality, exhibit transformative potential for advanced sensors and electronics. This review systematically examines their fabrication—including freeze-drying, supercritical drying, and 3D printing—alongside functionalization strategies (e.g., conductive nanofiller integration, crosslinking, and surface modification) that tailor mechanical, electrical, and interfacial properties. The hierarchical porous architecture enables exceptional performance in sensors: pressure/strain, humidity, gas, and biosensors. In electronics, they serve as flexible conductors, energy harvesters, supercapacitors, battery separators, electromagnetic interference shields and thermal insulators. Challenges persist in scalability, environmental stability, and interfacial compatibility, yet emerging solutions, such as in-situ functionalization and sustainable processing, promise to advance applications in wearable tech, IoT, and energy systems. Future directions prioritize multifunctional composites, AI-driven design, and scalable green synthesis to realize next-generation sustainable devices.