Zinc electrowinning from ammoniacal pregnant leach solution obtained by selective alkaline leaching of carbonate-containing smithsonite ore from Yahyalı, Kayseri, Türkiye, was investigated under additive-free conditions and in the presence of polyethylene glycol 2000 (PEG 2000), thiourea, and their combined addition. Under additive-free conditions, current efficiency reached a maximum of 86.4% at 400 A/m2, then decreased at higher current densities due to dendritic growth at cathode edges and increased hydrogen evolution. Individual additions of 1 g/dm3 PEG 2000 and 100 mg/dm3 thiourea as organic additives improved deposit morphology and current efficiency but were insufficient to suppress dendritic growth at elevated current densities. The combined addition of 1 g/dm3 PEG 2000 and 100 mg/dm3 thiourea at 100 A/m2 for 2 hours effectively suppressed dendritic growth and produced compact, uniform zinc deposits with a fine nodular structure, yielding a maximum current efficiency of ~95% and the lowest specific energy consumption of ~5.0 kWh/kg among the additive-containing conditions investigated. EDS analysis showed a zinc content of 91.11 wt% in the combined additive system, the highest among the conditions investigated, while XRD analysis showed reduced secondary phase intensities compared with additive-free and single-additive conditions. PLS composition was estimated from an XRF-derived mass balance rather than directly measured; the reported current efficiencies are apparent gravimetric values; and a complete Zn mass balance for the electrowinning stage was not established. These results demonstrate the potential of the combined PEG 2000 and thiourea additive system for zinc electrowinning from ammoniacal leach solutions derived from smithsonite ores.