8 figures, 3 tables.-- Supplementary information available.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/ The traditional chrome-based leather industry is facing several restrictions due to potential risks to the environment, especially for the formation and release of hazardous and carcinogenic Cr (VI). However, the leather produced from alternative organic tanning agents generally does not meet the market requirements due to the poor fixation of some of the conventional anionic post-tanning materials. Herein, we report on a pioneering, Cr-free strategy to produce high-quality leather. It comprises the use of a carbon-neutral, biomass-based aldehyde (BAT) tanning agent, efficiently fixed in the leather by means of novel terminal aluminum tanning treatment (TAT). In this treatment, Al (III) bonded with the excess oxygen-containing functional groups present in the BAT, post-tanning materials and collagen fibers. As a result, these connections created a robust crosslinking network, leading to leather products with similar (and in some cases superior) properties to those produced with the conventional Cr tanning procedure. For example, the tensile and tear strengths (19.78 N/mm2, 101.47 N/mm) were much higher than those of the Cr leather (7.13 N/mm2 and 43.12 N/mm). Therefore, these outstanding results, along with the carbon-neutral and environmentally-friendly features of our BAT-TAT strategy, are a step-change toward chrome-free leather production, which paves the way to ensuring the viable and sustainable development of the leather industry. This work was financially supported by the National Key R&D Program [grant number 2020YFE0203800] and the National Natural Science Foundation of China [grant numbers 22108297, 52073301]. Javier Remón is grateful to the Spanish Ministry of Science, Innovation and Universities for the Juan de la Cierva (JdC) fellowship [grant number IJC2018-037110-I]. Peer reviewed