Environmental and economic sustainability is an increasingly important priority in civil engineering. In this context, the stabilisation of clayey soils offers an effective strategy for reusing excavated materials, thereby reducing the consumption of natural resources and minimizing transport-related environmental impacts. Typically, excavated geomaterials are compacted in situ under unsaturated conditions and employed in the construction of infrastructure such as roads and railway embankments, levees, dams, and backfills. However, enhancing the mechanical behaviour of low-quality soils often requires chemical binders such as lime or cement, which undermine sustainability due to the high environmental impact of their production processes. Therefore, alternative solutions involving the use of industrial by-products need to be explored. This study investigates the potential of marble sawing sludge, a by-product of marble production with significant disposal challenges, as a novel chemical binder for the stabilisation of high-plasticity clays. After characterizing the sludge, its transformation through calcination was examined. The resulting binder was then used in clay-binder mixtures, which were subjected to compaction tests, swelling and oedometer compression tests, unconfined compression strength (UCS) tests along with total suction measurements. Furthermore, UCS tests over time combined with suction monitoring were conducted to evaluate the binder' s long-term effectiveness in soil stabilisation. The results demonstrate that stabilisation using this sustainable binder is very promising for geotechnical applications.