•The feasibility of using anhydrous sodium metasilicate as a geopolymer activator for soil stabilization had been verified.•The strengths of stabilized clay samples activated by a conventional activator and the ASM activator had been compared.•The effects of modulus ratio, content of activators, GGBS on the strengths of stabilized clay samples were evaluated.•The two-stage process of dissolution ofASM powder in geopolymer-stabilized clay was verified by the 29Si MAS-NMR results. This paper presents recent research on the use of anhydrous sodium metasilicate (ASM) powder as the alkaline activator of a one-part geopolymer binder for use in soil stabilization, to enhance the strength properties of soft clay. Geotechnical, mineralogical and microstructural tests were used to determine the performance of the geopolymer binder when mixed into an artificial soft clay. Comparison with the strength development of geopolymer-stabilized clay samples activated by a conventional sodium hydroxide activator and the ASM activator had been made. The effects of modulus ratio (SiO2/Na2O), content of the activators, as well as the GGBS content, water content, and curing time on the strength development of the geopolymer-stabilized clay samples were evaluated. The results indicate that the ASM powder alone is suitable as an alkaline activator to generate a one-part geopolymer binder for soil stabilization based on its high 28-d strength (4.2MPa) and its modulus ratio, which was in the optimal range (0.9–1.2). The microstructural analyses confirm the influence of the two-stage dissolution process of the hydrated amorphous alkali metal silicate powders on the strength development of the ASM-powder clay samples and the formation of the geopolymer gels. This study demonstrates that the ASM powder can be used to substitute for sodium hydroxide in generating a geopolymer binder, which can lead to more practical applications for geopolymer in soil stabilization.