Ground granulated blast furnace slag (GGBFS) has been widely used as a Portland cement replacement in concrete production. However, due to its intrinsic slow early hydration, GGBFS-rich (>50wt.%) Portland cements can exhibit delayed strength development, which limits the content of GGBFS used in concrete mix designs in engineering practice, therefore higher GGBFS are not typically utilised in industrial practice. In this study, it was investigated the effect of adding a Mg-Al layered double hydroxides (LDH) with a hydrotalcite type structure, on the hydration and mechanical performance of high-volume GGBFS (80 wt.%) blended Portland cement paste. The addition of LDH can effectively accelerate the early hydration of GGBFS blended cement. By adding 5 wt.% of LDH relative to the binder content, the compressive strength of GGBFS-blended Portland cement mortar was improved by about 10% after 1 day of curing, compared to the reference. Thermodynamic modelling, under the assumption that LDH primarily affects GGBFS reaction at later curing ages, indicated that LDH-addition promotes the generation of aluminium substituted calcium silicate hydrate (C-(A)-S-H) type gels and monosulphate, thereby enhancing strength development. This study demonstrates the potential of Mg-Al LDHs additions to control hydration kinetics and early age strength development of GGBFS-rich blended Portland binders.