Bio-waste-derived activated carbon (AC) is a promising electrode material for sustainable electrochemical double-layer capacitors (EDLCs), yet its environmental performance remains insufficiently quantified, particularly at the full-cell level. This study evaluates the sustainability of a prototype EDLC using AC derived from olive pits through a cradle-to-gate life cycle assessment (LCA). The assessment covers AC production, electrode fabrication, and cell assembly, combining primary laboratory-scale data with literature inventories and background databases. Environmental impacts were quantified using the Environmental Footprint 3.1 method, with functional units of 1 kg AC and, for the 34 F pouch-cell EDLC, 1 F of capacitance and 1 Wh of discharge energy. Results show that laboratory-scale AC production is highly energy-intensive, with thermal treatment as the dominant hotspot, resulting in a global warming potential (GWP) of 441.5 kg CO$_2$ -eq per kg AC. At the device level, electrode manufacturing dominates the environmental profile, mainly due to AC production, drying, calendering, and cell assembly. In the baseline case, EDLC impacts are strongly shaped by the laboratory-scale dataset. Scenario analysis reveals a pronounced scale effect. When higher-scale AC production inventories substitute the laboratory dataset, overall EDLC pro-
duction impacts decrease by over 80% with respect to the baseline. In these scenarios, GWP converges to approximately 5.6 × 10$^{−3}$–5.8 × 10$^{−3}$ kg CO$_2$-eq per F, and hotspots shift to electrode processing, assembly energy, and electrolyte supply. Overall, olive-pit-derived AC is a promising sustainable precursor for EDLCs; however, its advantage depends on efficient processing and large-scale production. This study provides a robust basis for sustainable bio-waste-based supercapacitor design.