Activated bleach systems have the potential to produce more efficient kinetically potent bleaching systems through increased oxidation rates with reduced energy cost and less time, hence causing less cellulose polymer chain damage or degradation than conventional hot peroxide bleaching. This article presents a study at the molecular level of a novel and more sustainable cationic bleach activator for cotton than aromatic-based cationic bleach activators using combined experimental and first-principles density functional theory (DFT) calculations. In this study, a novel and aliphatic-based cationic bleach activator, N-[4-(N,N,N)-triethylammoniumchloride-butanoyl] butyrolactam (TBUCB), was synthesized and applied for hot peroxide-cotton bleaching to optimize the bleaching conditions at lower temperatures. To improve the bleaching efficiency in the presence of TBUCB, the limitations of TBUCB, namely, the limitations of peracid generation in situ, have been identified using DFT calculations. First-principles density functional theory (DFT) calculations were performed to elucidate the reaction mechanism via identifying plausible transition state(s) of the nucleophilic attack of perhydroxyl anion (HOO–) at different carbonyl carbons and the advantages and limitations of the TBUCB activator for hydrogen peroxide bleaching for cotton. The results obtained showed that a whiteness index greater than 80 for cellulose can be achieved using an activated H2O2-TBUCB bleaching system at a lower temperature, providing reduced energy costs while maintaining the integrity of cellulose polymer chains.