This study explores the potential of using geopolymerised slag (GGBS) and sugarcane bagasse ash (SCBA) for stabilizing lithomargic soil subgrades. Through a series of compaction tests, the optimal dry density was achieved with varying dosages of SCBA while maintaining a constant GGBS dosage of 10% by weight of the soil. The sodium hydroxide (NaOH) and liquid sodium silicate (Na2SiO3) in calculated amounts were used to produce the geopolymeric aqueous solution. The UCS and CBR tests were conducted on both unstabilized and stabilized soil mixtures. The experimentations indicate that the strength of subgrade soil increases with the inclusion of SCBA up to a certain threshold (i.e., 15%), beyond which it diminishes, under a constant dosage of slag. This study also proposes a pavement design based on the Indian Roads Congress (IRC) guidelines for low-volume pavements, demonstrating significant reductions in total pavement thickness with maintained performance. The microstructural analysis is performed to understand the hardening performance upon geopolymer stabilization. Co-relationships between the strength parameters (UCS and CBR) were established, allowing for the development of a simple linear regression model to understand the relationship between the strength parameters of geopolymer stabilized lithomargic soil.