Recently, there has been an increasing interest towards the fabrication/finishing of bioactive materials using natural plant extracts, which can achieve a wide range of functional properties and environmental benefits. This study presents an environmentally benign bioactive finishing of wool fabric via the use of unexplored tannin-rich waste/fallen leaves extract of Chinese tallow/Sapium sebiferum L. through simple adsorption technique. Simple aqueous extraction followed by the evaluations of build-up properties on wool fabric using Chinese Tallow (CT) leaves extract were studied in due course of this study. Optimization of extraction and dyeing variables/conditions such as pH, temperature, CT concentration, and time were conducted using UV–Visible and reflectance spectral method. The nature of functional groups of the extracted dye were investigated through FT-IR spectral analysis with further in depth thermal analyses using TG and DSC measurements. Additionally, the extracted dye was subjected to quantitative analytical tests to check the relative amounts of total phenolics and flavonoid with respect to gallic acid and catechin equivalents, respectively. Build-up properties and fastness characteristics were studied in the presence and absence of mordants (two metal and one biomordant) under corresponding ISO standards. Results showed that wool fabric treated with CT leaves extract exhibit excellent antioxidant activity, good UV protection and high antibacterial activities against E. coli and S. aureus. The use of biomordant to alter the functional properties provide an eco-friendly method for wool finishing. In general, the treated wool fabric in this work has shown a promising future for the preparation of health and hygiene-related textile materials. •An environmentally friendly benign cleaner production procedure has been presented.•Waste/fallen leaves of Sapium sebiferum L. were used for natural dye production.•Extracted dye was characterized by UV–visible and FT-IR analysis.•Potential antibacterial and antioxidant wool fabrics were produced.•Finished wool fabric possesses excellent UV protective properties.