The addition of carbon nanotubes (CNTs) to cementitious nanocomposites have demonstrated significant mechanical performance enhancements, however, there has been only limited research of the effects of CNTs upon hydration kinetics. Isothermal calorimetry was used to study in detail (i) CNT dispersion with and without a polycarboxylate-based superplasticiser, (ii) CNT dose at 0.05–0.25 wt% of cement, and (iii) CNT dispersion quality upon cement hydration. Results show a 45-min acceleration and 17% increase in principal hydration peak at a CNT dose of 0.1 wt% without superplasticiser, indicating enhanced nucleation with CNTs. Varying CNT dose, delaying effects of the superplasticiser dominated, although there was an increase in hydration peak of 17% with 0.25 wt% CNTs. Finally, it was found that CNT content, not ‘good’ or ‘poor’ dispersion quality, had a greater effect upon the overall nanocomposite hydration and microstructural development, facilitating further optimisation of CNT dispersion and microstructural development for CNT-cement nanocomposites.