<p>Weaning marks a critical life-history transition in mammals, shaped by maternal investment strategies, offspring condition, and environmental constraints. In Galápagos sea lions (<i>Zalophus wollebaeki</i>, GSL) weaning age is highly variable, with some individuals continuing to suckle well into adulthood (supersucklers). Using 20 years of both suckling observations and mark-recapture data from 1890 individuals, we applied multi-state capture-recapture models (MSCRM) to investigate weaning age, and logistic regression models to explore the drivers of supersuckling in GSL. We examined age at weaning from both the maternal (age, birth interval, and pup condition at birth) and offspring perspective (sex, early growth), and environmental variability (Oceanic Niño Index [ONI]). We found that weaning is most likely to occur between the ages of 1.5–4.5 years with 95% of offspring weaned by 4.5 years of age. El Niño conditions during early life influence weaning age and the probability of offspring becoming supersucklers in later life. Longer birth intervals were associated with later weaning, while offspring sex had no influence. No intrinsic maternal or offspring predictors of supersuckling were identified warranting further investigation to better understand this behaviour. Our results show that MSCRMs are an effective means of identifying the occurrence of more cryptic and anecdotal behaviour and highlight the complexity of weaning behaviour in an income-breeding mammal with a prolonged lactation period. Finally, we propose that weaning age in GSL may not be wholly explained by mother–offspring conflict, and that further investigation considering factors not included in this study is needed.</p>