Background: Osteoporosis is a metabolic bone condition that increases fracture risk. This study aimed to examine whether dicalcium silicate (C₂S) promotes bone-forming potential of bone marrow mesenchymal stem cells (BMSCs) via Wnt/β-catenin signaling pathway and enhances bone repair in osteoporotic rats. Methods: Rat BMSCs were isolated and identified. Cell counting kit-8 method was employed to evaluate proliferation of BMSCs. BMSCs were divided into control, C₂S, and C₂S + Wnt inhibitor (Dickkopf-1 (DKK-1)) groups. Mineralization was evaluated through alizarin red staining. Quantitative real-time polymerase chain reaction (PCR) and western blot assays were conducted to assess messenger ribonucleic acid (mRNA) and protein levels of β-catenin, Runt-related transcription factor 2 (Runx2), osteopontin (OPN), and osteocalcin (OCN). An osteoporotic bone defect rat model was established. The animals were randomly divided into model, BMSC, and C₂S-BMSCs groups. Bone regeneration was analyzed via micro-computed tomography (CT) and histological staining. Immunohistochemistry analyzed β-catenin, Runx2, OPN, and OCN expressions in femur tissues. Results: BMSCs were successfully isolated and identified. 100 μg/mL C₂S was used for subsequent experiments. In vitro, C₂S significantly increased mineralized nodule formation and increased the mRNA and protein levels of β-catenin, Runx2, OPN, and OCN (p < 0.001). These effects were considerably attenuated by DKK-1 (p < 0.01). In vivo, BMSCs and C₂S-BMSC scaffolds improved bone regeneration, with C₂S-BMSCs having better repair effects (p < 0.01), and higher expressions of β-catenin, Runx2, OPN, and OCN (p < 0.05) than BMSCs. Conclusions: C₂S-induced stimulation of Wnt/β-catenin pathway stimulates BMSC osteogenesis, thereby facilitating osteoporotic bone regeneration and offering a promising therapeutic approach for osteoporosis-related bone defects.