The application of chemical stabilizers and fibres for the stabilization of weak soil subgrades can mitigate the cost and CO2 emissions associated with pavement construction. The present study evaluates the feasibility of improving clay and sand subgrades using a calcium-based stabilizer (CBS)-commercial name: RBI Grade 81-and synthetic fibre-polyester fibre for building economic and sustainable pavements. Two soils, i.e. silty clay of low plasticity and silty sand, were stabilized and reinforced with independent and combined proportions of the CBS and polyester fibre. The test program included plasticity, compaction, advanced cyclic triaxial (ACT), and California bearing ratio (CBR) tests. The experimental and theoretical resilient moduli were determined using ACT and CBR tests, respectively. Subsequently, scanning electron microscopy and X-ray diffraction tests were then conducted to assess the microstructural and mineralogical changes in the soils due to the stabilization and reinforcement. Flexible pavements were designed with experimental and theoretical resilient modulus (MR). A good correlation was developed between the CBR and experimental MR. The results of the study demonstrate a significant overestimation of MR by the theoretical method. It was seen that with up to 186% higher CBR, 228% higher experimental MR, 96% higher theoretical MR, 230% higher traffic benefit ratio, 22% savings in construction cost, and 24% reduction in greenhouse gas emissions, the stabilized soils exhibited superior performance. The study thus demonstrates that the CBS combined with polyester fibre can be used for economical and sustainable pavement construction.