<p>Expansive soils are utilised in many civil engineering infrastructures such as levees, the core of earthen dams, canals, and compacted clay liners. However, these soils are prone to desiccation cracking, which can lead to contaminant transport, reduced soil shear strength, increased compressibility, enhanced soil weathering, and rainfall-induced landslides. Conventional stabilisation techniques often raise sustainability concerns, such as increased alkalinity, carbon footprint, and harmful chemicals leaching. Hence, the present research explored an environment-friendly sustainable way for desiccation crack mitigation by utilising natural fibres. A series of shrinkage drying and unconfined compressive strength tests were conducted on expansive soil mixed with the different percentages (0%, 0.25%, 0.5%, 0.75%, and 1%) of coir fibres and banana fibres. A scale effect of soil samples on crack formation was also examined. Digital image analysis (DIA) was used to calculate the crack intensity factor (CIF) and other crack parameters. Results showed that adding 0.25–1.00% coir and banana fibres reduced the desiccation cracks by 66–92% and 52–80%, respectively. Coir fibre’s rough surface texture and higher adhesiveness than banana fibre were responsible for their better performance. Fibre-reinforced soil exhibited faster water loss and higher volumetric shrinkage due to the bleeding mechanism. The unconfined compressive strength of fibre-reinforced soil increased by 43.5% with 0.25% coir fibres and 23.7% with 0.25% banana fibres, but showed a negative trend at higher percentages of fibres, reaching the lowest strength and most ductile response at 1.00% fibre content. The optimal fibre content of 0.50% is recommended for balancing crack mitigation, shrinkage control, and strength improvement. This study concludes that natural fibre addition provides an effective and sustainable solution for managing desiccation cracks in expansive soils.</p>