The past decade has seen the progressive contribution of cellulose-based nanocomposites in realizing sustainable, multifunctional, and high-performing electronic devices and functional materials. The multidimensional properties of nanocellulose are complemented and further enhanced by combining with other functional nanomaterials such as polymers, carbonaceous materials, metals, and other inorganic materials in various nanohybrid architectures. The sustainability of nanocellulose as a raw material is complemented with scalable and energy-efficient synthetic methodologies in realizing sustainable and fully recyclable electronics and functional nanomaterials. Furthermore, the flexibility and biocompatibility of nanocellulose-based substrates make them ideal platforms in Fleco electronics, biomimetic surfaces, and adaptable materials. The realized synergistic effects make them essential components in various sensors and electronic devices, packaging materials, adsorbents and filtration membranes, biomedical materials such as wound dressings and tissue engineering scaffolds, and automotive and aircraft parts, among others. Finally, their significant role in flexible, wearable, and biomimetic devices and in sustainable materials is unprecedented.