Zoos and aquariums are well placed to connect visitors with the issues facing biodiversity globally and many deliver interventions that seek to influence visitors’ beliefs and behaviors with respect to conservation. However, despite primary studies evaluating the effect of such interventions, the overall effect of engaging with zoos and the factors that influence this effect remain unclear. We conducted a systematic review to investigate the effect of zoo‐led interventions on knowledge, beliefs (attitudes, intentions, self‐efficacy, and social norms), and behavior among zoo visitors. These outcomes were identified using the Theory of Planned Behavior as a theoretical lens. We identified and described the nature of zoo‐led interventions in 56 studies and used the behavior change technique (BCT) taxonomy to identify 6 specific BCTs used in interventions to date. Multilevel meta‐analyses revealed a small to medium positive effect of engaging with zoo‐led interventions on outcomes (d+ = 0.40, 95% confidence interval = 0.28–0.51). Specifically, visitors were more knowledgeable about conservation issues, held more favorable attitudes toward conservation, and reported being more likely to act for the benefit of biodiversity. No evidence of publication bias was present. Effect sizes were, however, heterogeneous and subgroup analyses revealed that the nature of the intervention or type of outcome did not explain this variance. Larger effects were, however, found in studies conducted at a single institution relative to research at multiple institutions and studies that used within‐participant designs relative to between‐participant designs. Taken together, these findings demonstrate how behavior change frameworks can be used to describe zoo‐led interventions and supports the assertion that zoos and aquariums can promote changes in beliefs and behaviors that may help protect biodiversity.