The rheological properties of concrete are crucial for its workability and mechanical performance, but the requirements may conflict at various stages of construction. For example, 3D concrete printing demands low yield stress and viscosity for pumping and extruding, while requiring higher static yield stress post-extrusion to prevent collapse. Therefore, it is necessary to regulate the rheological properties to balance these conflicting requirements. Magneto-rheological control is an innovative approach that involves adding magnetic particles to cementitious materials and applying an external magnetic field. This approach offers new possibilities for the active regulation of the rheological properties of cementitious materials. However, the effects of magnetic fields and magnetic particle additions on early microstructure and hydration behavior are not fully understood. To address this gap, this study investigates the impact of magneto-rheological response on the early hydration and microstructure in cement paste. The results show that the magnetic field induces a stronger magneto-rheological response with higher water to cement ratios and increased particle content. While it does not alter early hydration products, it negatively affects early microstructural compactness by creating weak zones between clustered magnetic particles. These findings contribute to a better understanding of magneto-rheological control and its potential in construction applications.