This paper reports on designed non-fired clay mixes for sustainability and low carbon use. Ground Granulated Blastfurnace Slag (GGBS), an industrial by-product, was used as a partial substitute for conventional stabiliser (Lime or Portland cement) to stabilise Kaolinite Clay (KC) and Lower Oxford Clay (LOC), for sustainable and low carbon non-fired clay building material production. Although GGBS has been used extensively in concretes to reduce the carbon footprint, there is an unexplored potential for its use as a cement replacement for stabilised soil production. The benefits of using GGBS in non-fired clay building material development include lower emissions of greenhouse gases and improved durability. The parameters considered under this study are: (1) material characterisation, (2) unconfined compressive and (3) durability. For the assessment of durability, a MX 2000VJ Tech multi-channel data logger equipped with a digital displacement transducer and computer device was employed to monitor the linear expansion behaviour of the stabilised test specimens. The 90-day unconfined compressive results for the test specimens showed that there is significant strength gain (up to 5 N/mm2) for all the stabilised mixtures. The lime-activated GGBS stabiliser has significantly higher influence in the strength gain compared to the equivalent PC-based system. These results suggest that there is potential in using Lime or Portland cement activated GGBS blend for the stabilisation of natural clay soil for sustainable and low carbon building materials production.