Herein, we report the development of a highly efficient activated porous acid catalyst using Psidium guajava (guava) leaves as the precursor. The synthesis involved chemical activation with ZnCl2 and sulfonation with 4-benzenediazonium sulfonate, resulting in the AC-X-PhSO3H catalyst, optimized by varying ZnCl2 ratios (X = 1, 2, 3). Comparative characterization using BET, SEM, XRD, FT-IR, and TGA revealed that AC-2-PhSO3H, pyrolyzed at 500 °C, exhibited exceptional efficiency with a maximum surface area of 492.97m²/g and a sulfur density of 4.23wt.%. Using AC-2-PhSO3H as the catalyst, we achieved a remarkable Jatropha curcas oil (JCO) conversion (98.3 ± 0.3%) to biodiesel under optimized reaction conditions (20:1 methanol to oil molar ratio, 10wt.% catalyst loading, 100 °C, 50min) and FAME content of 98.04%, as confirmed by ¹H-NMR spectroscopy. The estimated cost of biodiesel production was $0.87 per litre, largely due to the notable reusability of the catalyst (82.9 ± 0.2% JCO conversion in the 6th run) without additional treatments, indicating significant commercial applicability and enhanced stability.