The transition towards low-carbon construction materials necessitates the redesign of high-performance cementitious systems traditionally reliant on high volumes of Portland cement. Engineered Cementitious Composites (ECC), while offering excellent ductility and crack control, contribute significantly to CO₂ emissions due to their high cementitious content. Limestone Calcined Clay Cement (LC3), a ternary binder composed of Portland cement, calcined clay, and limestone, presents a promising alternative for reducing the environmental impact of ECC. To explore this potential, this study investigates the influence of superplasticiser type and dosage on the fresh and hardened properties of LC3-based ECC mixtures, aiming to optimize rheological behaviour and strength development for sustainable, high-performance composites. ECC mixes were prepared with a 55% replacement of Portland cement by LC3, including Portland cement, calcined clay, and limestone. Calcined clay with a reactivity value of 410 J/g of SCM, as per ASTM C1897, was used to produce the LC3. Four commercial superplasticisers were used at dosages of 0.5%, 0.75%, 1.0%, and 1.2% by weight of binder. Fresh properties, including slump, deformation factor, flow time, and rheology, as well as the compressive strength of these mixtures, were tested to determine the compatibility of superplasticiser to obtained desired fresh and hardened properties in the ECC mixes. Superplasticiser type and dosage critically influence rheology and mechanical performance, with higher dosages enhancing workability, deformation, and flow time, leading to improved particle dispersion and compressive strength, highlighting the importance of admixture optimization in LC3-based ECC for sustainable, high-performance applications.