Rapid urbanization and technological advancement have led to worrisome challenges associated with increasing waste production, and its management is overly burdensome. Indonesia annually produces 100,000 tons of leather tanning waste (LTW) and 2600 tons of waste capiz-shell (WCS). This study proposed a zero-waste approach by utilizing WCS as the catalyst for biodiesel production from LTW. Based on the characterization results, the WCS-based catalyst is proven to possess high porosity and comparable catalytic activity to the other heterogeneous catalysts. The maximum yield of FAEE was 93.4 wt%, obtained at 60 °C, 4 h reaction time, 3 wt% catalyst loading, and ethanol to LTW molar ratio of 6:1. High FAEE yield (> 90 wt%) can be obtained by reusing the WCS-based catalyst until the third reaction cycle. To examine the feasibility of this zero-waste act, a simple viability study was also performed by comparing this process to the conventional basic transesterification process.