Background An increasing number of studies are investigating the efficacy of mindfulness-based interventions (MBIs) for weight loss and obesity-related eating behaviours. However, the results of past reviews are inconsistent. Objective To clarify these inconsistencies, we conducted a comprehensive effect-size analysis to evaluate the efficacy of MBIs on weight loss and eating behaviours. Data source Data sources were identified through a systematic review of studies published in journals or as dissertations in PsychINFO, PubMed, CINAHL, Web of Science, Medline and Scopus, ProQuest or OATD from the first available date to March 10, 2017. Review methods A total of 18 publications (19 studies, n = 1,160) were included. Results Mean weight loss for MBIs at post-treatment was 6.8 and 7.5 lb at follow-up. In pre–post comparisons, effect-size estimates suggest that MBIs are moderately effective for weight loss (n = 16; Hedge's g = .42; 95% CI [.26, .59], p < .000001) and largely effective in reducing obesity-related eating behaviours (n = 10; Hedge's g = .70; CI 95% [.36, 1.04], p < .00005). Larger effects on weight loss were found in studies that used a combination of informal and formal meditation practice (n = 6; Hedge's g = .55; CI 95% [.32, .77], p < .00001) compared with formal meditation practice alone (n = 4; Hedge's g = .46; CI [.10, .83], p < .05). Conclusion Results suggest that MBIs are effective in reducing weight and improving obesity-related eating behaviours among individuals with overweight and obesity. Further research is needed to examine their efficacy for weight loss maintenance.