<p>Biopolymer treatment has emerged as an environmentally sustainable approach to improve the mechanical performance of industrial byproducts, such as fly ash (FA), yet their energy-based performance remains underexplored. This study investigates the energy absorption, energy retention, and energy improvement ratio of biopolymer-treated FA to evaluate their long-term degradation performance. Biopolymer dosages ranging from 0.25 to 1.25% xanthan gum (XG) and 0.10–0.50% guar gum (GG) were evaluated, and stress–strain data from monotonic compression tests were used to compute the energy parameters. The optimum dosages were identified as 0.75% XG and 0.50% GG, at which the energy absorption increased by 21 times and 32 times, respectively, compared to untreated FA. The curing period analysis showed progressive enhancement, with energy improvement ratios of 31 for XG-treated FA and 48 for GG-treated FA after 100 days. Durability was assessed under cyclic wetting–drying and chemical exposure, including exposure to acid, sulphate, and chloride solutions for up to 100 days. Cyclic wetting-drying caused a 52–60% decline in energy absorption, while acid and sulphate exposures produced reductions of 45–52% and 42–53%, respectively, and chloride exposure resulted 43% decrease in energy absorption. GG-treated FA exhibited higher early-stage resistance across all exposure conditions, whereas XG-treated FA showed slightly better long-term energy retention under sulphate and chloride conditions. These findings confirm that biopolymer stabilisation significantly enhances the energy absorption capacity and environmental endurance of FA, demonstrating its potential as a sustainable geomaterial for long-term engineering applications.</p>