Industrial and urban wastes have been generated over time due to urban development with severe environmental and health implications. This paper reports the valorisation of waste and industrial by-product (magnesium oxide waste – MG1 and Ground Granulated Blast furnace Slag – GGBS) to develop an alternative cementitious binder for suppressing swelling in high sulphate bearing soils due to the formation of a highly expansive crystalline hy drate (ettringite) upon treatment with Portland Cement – PC or lime. Cylinder test specimens were developed us ing three MG1:GGBS proportions by weight (10:90, 20:80 and 30:70) to stabilise a natural Gypsum marl soil (GM) containing high levels of sulphate at varying stabiliser dosages (6, 8 and 10 wt%), with PC as the control binder. UCS, Linear Expansion and SEM investigations were employed to assess the engineering suitability of the MG1:GGBS stabilised GM cylinder test specimen. Results suggest the viability of producing an alternative cemen titious binder using up to 30 wt% MgO-waste to successfully activate GGBS at stabiliser dosages of 6–10 wt%. From a mechanical perspective, the MG1:GGBS stabilised GM soil was 1.5–3 times more than the control at 28 days moist curing age, while the resistance to linear expansion produced near-zero swellings (0.13%–0.2%) after 56 days, in comparison with the control of 3.2%. SEM micrographs showed a more compact structure with lesser voids and no morphology of ettringite. This new technology is expected to mitigate the environmental concern of using PC and promotes sustainable techniques of reusing industrial by-product materials for stabilising sulphate soils.