The potential use of locally sourced ground granulated blast-furnace slag (GGBFS) and commercial sodium sulfate (Na2SO4) in the development of an eco-friendly sulfate-activated binder (SAB) was investigated in this study. The influence of Na2SO4 contents (1.5, 3.0, 4.5, 6.0, and 7.5% by mass of GGBFS) as a crucial sulfate activator on mechanical strength and durability performance of the SAB samples was evaluated through the tests of compressive strength, porosity, chloride ion penetration, and ultrasonic pulse velocity. The correlations among these properties were also established and discussed. The experimental results show that the Na2SO4 content had significant influences on both the strength and durability of the SAB samples. The porosity and chloride ion penetration were reduced as increasing the Na2SO4 content. Meanwhile, increasing the Na2SO4 content increased the compressive strength and ultrasonic pulse velocity of the SAB samples. Furthermore, the test results point out that using 7.5% Na2SO4 provided a significant improvement in the mechanical strength and durability performance of the newly developed SAB.