The sustainable utilization of agricultural side streams is essential for advancing biorefinery technologies that can promote a sustainable bioeconomy. Arising as a waste stream from cereal grain processing, oat husks (OH) are a promising biomass feedstock for the circular bioeconomy, offering the potential for the production of a range of valuable biopolymers and chemicals. As other lignocellulosic biomasses, OH possess a complex hierarchical structure, with distinct layers containing cellulose, lignin, hemicellulose, and other compounds interacting at multiple scales. This structural complexity leads to biomass recalcitrance, a significant challenge for efficient fractionation, as it requires the use of multiple solvents to separate and selectively extract different components. Here, we compare two multi-step fractionation methods for OH: a conventional acid-alkaline-bleaching process targeting lignin and cellulose, and a greener approach using more benign solvents coupled with additional steps, targeting also lipids, oligosaccharides and silicates. Comprehensive characterization was performed to evaluate the efficiency of both approaches. FTIR spectroscopy and TGA were employed throughout the process to monitor changes in the chemical composition and thermal stability of the intermediate products, providing insight into the effectiveness of each fractionation step in separating the targeted compounds. The morphology of the various fractions obtained was examined using SEM. Further chemical characterizations included NMR for lignin, XRD for cellulose, and others. Collectively, the results demonstrate the efficacy of the proposed green fractionation process, improving the mass efficiency of the OH biorefinery while also providing chemicals and biopolymers with preserved properties, that can be employed in various sustainable applications. Further challenges remain to improve the sustainability of the process, particularly regarding the recovery and reuse of solvents. Nonetheless, the promising results obtained highlight the potential of green fractionation strategies for the development of high-value biobased materials from lignocellulosic side streams, paving the way for further advancements in sustainable biomass processing.