To address the high carbon emissions generated during the production of cement, lime, and other traditional soil stabilizers and to promote the resource utilization of industrial solid waste, this study proposed a low-carbon loess stabilization scheme using tuff powder (TP), fly ash (FA), and ground granulated blast-furnace slag (GGBS) activated by alkaline solutions to fully substitute conventional cement and lime. A series of macroscopic tests, including unconfined compressive strength, water immersion, and triaxial shear tests, were carried out on stabilized loess. Combined with microcharacterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopic testing, this study systematically evaluated the mechanical performance, water stability, and microstructural evolution of stabilized loess and quantified its global warming potential (GWP). Macroscopic test results reveal that the composite binder consisting of 15% multi-source solid waste (TP:FA:GGBS) = (1:1:3), 3% NaOH, and 3.2% Na₂SiO₃ (relative to solid waste mass) delivers the optimal comprehensive performance of stabilized loess. Alkali activation significantly accelerates early strength development, and both compressive and shear strengths are markedly improved compared with samples treated solely with solid waste. Furthermore, decreasing the activator modulus further enhances mechanical properties and water resistance. Microscopic characterizations demonstrate that alkali activation stimulates the pozzolanic reaction of active components in solid waste, generating cementitious gels that bind soil particles and unreacted solid waste to form dense network matrices. As a fine filler, TP also acts as a nucleation sites for hydration product crystallization, which facilitates the formation of cementitious phases.