By calcination and sulfurating Chestnut shell biomass (CNS), a solid acid catalyst was synthesized. In the preparation of the catalyst, a range of calcination temperatures (150 °C–350 °C) and time 2 h, a range of sulfonation temperatures (80 °C–160 °C), and a range of times (1–6 h) were examined in order to determine the effect on catalytic activity. The CNS300–SO3H catalyst was characterized by Brunauer-Emmett–Teller (BET), Fourier transforms infrared (FT–IR) spectroscopy, N2–adorption and desorption, and thermogravimetric analysis (TGA). A higher acid density (8.626 mmol/g–1) was found with the CNS300–SO3H catalyst, as well as a higher surface area (1198.12 m2/g–1). As part of the catalytic activity test, prepared catalysts were tested for their ability to catalyze the esterification of oleic acid with ethanol. Results revealed that a sulfonated activated carbon–CNS-derived acid catalyst is capable of esterifying oleic acid to about (95.25%) conversion. Chestnut-prepared catalysts showed better performance due to their high specific surface areas. Furthermore, the hydrophobic nature of the CNS300–SO3H catalyst made it stable for up to nine cycles of recycling. Catalyst is recyclable, and cheap feedstock makes the overall process more cost-effective and environmentally friendly.