<p>Geopolymer-based concrete composites are emerging as highly promising low-carbon composites, gaining increased global interest due to their sustainability and performance advantages over the conventional concrete composites. However, brittle nature of geopolymer composites limits their practical usage, necessitating the development of fibre-reinforced geopolymer concrete. This study investigates the effect of incorporating glass wool fibre (GWF) and nylon fibre (NF) on the mechanical properties of ambient cured fly ash-slag based geopolymer concrete (GPC). The test results exhibited that the workability of GPC decreased with the addition of GWF and NF. A slight decrease in the compressive strength of GPC was observed upon the incorporation of GWF and NF. However, at an optimal dosage of 1.0% GWF, the splitting-tensile and flexural strengths improved by approximately 16.7% and 15.3%, respectively. The optimal inclusion of 1.5% NF resulted in a significant improvement in the mechanical performance, with approximately 47.8% and 83.8% increase in splitting-tensile and flexural strengths, respectively. It was observed that GPC reinforced with GWF exhibited greater water penetration than that reinforced with NF. The microstructural analysis conducted using scanning electron microscopy (SEM) indicated that the tangential cracks that were evident at aggregate boundaries caused by internal stresses were arrested effectively within the matrix, leading to overall enhancement of splitting-tensile and flexural strengths of fibre-reinforced GPC mixes. Moreover, the life cycle assessment (LCA) showed that the global warming potential of fly ash-slag based GPC was approximately 67.2% less compared to that of ordinary Portland cement (OPC) concrete.</p>