Long term sustainability requires the elimination of waste products and their integration in the circular economy according to goals set by the European Union. Such is the case with Tetra pak one of the most extensively used food packaging materials in the world. More than half of the Tetra pak packaging ends up in the landfills due to the complicated disposal that requires special processing plants. The objective of this study is to investigate recycled cellulose (rCell) that has been separated from polypropylene and aluminum in the industrial processing plant as a structural filler for functional biocomposites. Cellulose-based waste products are widely used as filler materials for the composites classified as wood-plastic composites (WPC) and are one of the leading materials for sustainable building materials, furniture and packaging industry. We have selected one of the most promising bio-based and biodegradable polymers poly(butylene succinate) (PBS) that has comparable mechanical properties to polyethylene and polypropylene as a matrix for the composites. Thus, we propose a novel application route for rCell obtained during Tetra pak recycling process and evaluate its performance. High filler loading from 10 to 50 wt% has been used in the melt blending process to prepare 5 compositions that contain 55–75% bio-based carbon content. Life cycle inventory has been combined with excessive thermal and mechanical analysis to access the suitability of the composite for various application including submerging in water. The addition of 50 wt % of rCell into PBS leads to improvement of the hardness of the composites. Further, the rCell composites were found to have much higher Young’s modulus compared to pristine PBS. The dynamic mechanical analysis showed that the storage modulus and the loss modulus were significantly enhanced in measured temperature range between −70 and 70 °C. The PBS/rCell composites were biodegradable in soil under composting conditions. Scanning electron microscopy analysis of fractured composites’ surfaces testifies the filler agglomeration process in the PBS/rCell composites and generation of voids, but the FTIR measurements indicate the generation of hydrogen bonding between the polymer and cellulose components. TGA evidence the increase in thermal stability of the rCell after incorporation in the PBS/rCell composites.