Background <p>Identity, representations individuals hold about themselves, drives health behavior change, influencing both health-promoting and health-compromising behaviors. This mixed-methods systematic review synthesizes interventions directly targeting physical activity (PA)- and/or smoking-related identities to promote PA and smoking cessation in individuals aged 12&#xa0;years and over. It also examines the effects of these interventions on identity and behavior, as well as mediators or moderators of effectiveness.</p> Methods <p>A comprehensive search across nine databases identified 5801 records, with 19 reports (20 studies) being included. Two independent reviewers extracted data and assessed study quality using the Mixed Methods Appraisal Tool.</p> Results <p>Four types of identity-related interventions were identified: possible-self interventions, multi-component interventions incorporating identity components, possible-self avatar games, and identity-challenge interventions. Intervention effectiveness was mixed: nearly half of the studies reported significant positive effects on PA- and smoking-related identities and behaviors, while others found no significant differences. No significant negative effects were reported. Although results seem similar for both behaviors, more studies focused on PA, complicating direct comparisons. One study suggested that integrating PA promotion and smoking cessation into a single intervention could be beneficial, but further research is needed. Identified mediators and moderators include self-efficacy, planning, and consideration of future consequences.</p> Conclusions <p>Overall, identity-related interventions show promise for PA promotion and smoking cessation, but optimal design and operationalization remain uncertain. Tailoring these interventions to individual characteristics may enhance effectiveness and contribute to public health.</p> Systematic review registration <p>Open Science Framework <a href="https://osf.io/avtx4/">https://osf.io/avtx4/</a></p>