Lignin's polyfunctionality is evolving into alternative bio-based catalysts from under-used agro-industrial waste. To promote safe and eco-conscious disposal of these residues, maleated lignin catalyst (MLC) was prepared via simple and efficacious process, and used as a sustainable heterogeneous catalyst for the O-acetylation of SA (salicylic acid). Response surface methodology (RSM) built on Box-Behnken design of experiment (BBD) has reliably established the influence of reaction parameters on the catalytic properties of MLC. The characterization findings reveal stable yet efficient functional reactive sites on MLC, with an acid density of 4.92 mmol.g⁻¹ and BET surface of 1.37 m²/g. With only 4% MLC, high activity was achieved (95.14%) with short reaction time and low temperature (30 min, 60 °C), and an Ea of 56.11 kj.mol⁻¹. Upon reusability, the MLC was characterized by FTIR, XRD, TGA, SEM, BET, etc., and 57% of its catalytic activity was retained after 5 cycles, with high stability and no meaningful mass loss. The BBD model was statistically significant and exhibited good agreement between the predicted and actual yield. The adopted coupling of experimental and theoretical approaches for the first time in lignin-based catalysts can promote beneficial rational design and implementation of lignin catalysts in green chemical synthesis.