Black cotton (BC) soil poses threats to build structures owing seasonal volumetric changes. The production of fly ash (FA) and bagasse ash (BA) increasing abundantly, and their improper disposal poses detrimental effects on the environment and human health. This research aims to develop sustainable, novel, optimum binary blend by using FA and BA to improve the strength characteristics of the BC soil after curing periods of 7, 14, and 28 days. BA was mixed in different ratios by dry weight of FA to obtain the optimum binder based on maximum UCS. The optimum binder comprising of 80:20, mix by dry weight of BC soil in varying proportions. The effects of mix show significant changes in the geotechnical and mechanical properties of BC soil. Research shows that swelling features reduces alters into non-swelling soil. The soil transitions from a plastic to a brittle state. The results revealed that MDD, UCS, CBR and STS increases significantly with curing periods. The mineralogical and microstructural test carried out using XRD and SEM, which supports the creation of cementitious complex and development of a dense matrix. The results state that utilized binder to stabilize BC soil is suitable for civil infrastructure specially pavement and foundations.