Display omitted •Engineering properties and microstructure of the composites are investigated.•The positive and negative roles of PVA fibres in the composites are revealed.•This study promotes the recycling of industrial wastes (GGBFS and FA).•This study serves as an important reference for engineers and designers. Alkali-activated ground-granulated blast-furnace slag (GGBFS) and fly ash (FA) geopolymers are sustainable alternatives to cement. The incorporation of polyvinyl alcohol (PVA) fibres can help minimise their shortcomings, such as drying shrinkage and brittleness, but may lead to other negative effects. Only a few studies have focused on geopolymer composites based on PVA-fibre-reinforced binary phases (GGBFS and FA). The positive and negative roles of PVA fibres in the performance of composites have not been systemically investigated in previous studies. To promote the application of the composites, the mechanical properties, workability, durability, high-temperature resistance, fibre dispersion, phases, and microstructure of composites with 0, 0.3 and 0.6 vol% of PVA fibres were systematically investigated in this study. The results showed that the incorporation of PVA fibres significantly increased the flexural and splitting tensile strengths of the GGBFS- and FA-blended and single FA-based composites at ambient and high temperatures, and the drying shrinkage was significantly reduced. On the other hand, PVA fibre incorporation caused a decrease in the compressive strength, flowability, consistency, sorptivity, and chloride penetration of the composites; however, the values are still acceptable in construction. Compared to the single FA-based composites, the GGBFS- and FA-blended composites showed improved mechanical properties, sorptivity, chloride resistance, and high-temperature resistance owing to their decreased porosity. This study serves as an important reference for engineers and designers for the use of green composites.