Low-carbon cementitious materials (LCCM) served as the primary binder, river sand was used as fine aggregate, and crushed stone acted as coarse aggregate for concrete preparation. Concrete made with sulphoaluminate cement was used as the control sample. A systematic investigation was conducted into the early hydration characteristics, pore structure, and mechanical properties of the developed concrete containing LCCM under natural curing. To characterize the types, quantities, and micro-morphologies of early hydration products, X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), chemically bound water analysis, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were employed. Additionally, nuclear magnetic resonance (NMR) was utilized to analyze the pore structure of the concrete containing LCCM, focusing on porosity and pore size distribution. Regarding mechanical performance, the compressive strength and failure mode of early-age concrete were evaluated, and the relationships between pore structure and compressive strength, as well as the influence mechanisms of hydration products on compressive strength, were thoroughly examined.