Coal fly ash, an abundant industrial waste, was valorized for the synthesis of bromosodalite through a hydrothermal process. The synthesized material was subsequently acid-treated to generate catalytically active acidic sites, transforming it into a heterogeneous solid acid catalyst. The structural and morphological properties of the catalyst were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The acid-treated bromosodalite was then evaluated as a heterogeneous catalyst for the esterification of L-ascorbic acid with stearic acid to produce ascorbyl stearate, a value-added ester widely used in food, cosmetic, and pharmaceutical applications. The catalytic performance demonstrated successful esterification under heterogeneous conditions, offering a sustainable alternative to conventional homogeneous acid catalysts. The use of fly ash–derived bromosodalite not only reduces environmental waste but also overcomes drawbacks associated with homogeneous catalysis, such as corrosion, difficulty in catalyst recovery, and waste generation. This study highlights the potential of waste-derived solid acid catalysts for green and efficient esterification processes.