BACKGROUND: Sedentary behavior and physical inactivity may increase the risk of obesity. This systematic review and meta-analysis aimed to investigate: i) the prevalence/incidence of sedentary behavior and physical inactivity, ii) the association of sedentary behavior and physical inactivity with obesity, and iii) the objective and subjective measures, diagnostic criteria, and cut-off points to estimate sedentary behavior and physical inactivity in adults and older adults with obesity. METHODS: We conducted a systematic review and meta-analysis in PubMed, Scielo, Lilacs, and Cochrane Library databases. A meta-analysis of a random-effects model was performed to estimate the combined prevalence of sedentary behavior and physical inactivity and their association with obesity. RESULTS: Twenty-three studies involving 638,000 adults and older adults were included in the systematic review. A meta-analysis was conducted with 111,851 individuals with obesity. The combined prevalence of sedentary behavior was 31% (95% CI, 23-41%), and physical inactivity was 43% (95% CI, 31-55%). Significant associations between obesity and sedentary behavior (OR 1.45, 95% CI, 1.21-1.75) and physical inactivity (OR 1.52, 95% CI, 1.23-1.87) were found. Nine studies have used objective measures to assess physical activity levels, such as accelerometers and pedometers, whereas fourteen applied subjective methods and self-reported questionnaires. CONCLUSIONS: As expected, we found elevated rates of sedentary behavior and physical inactivity in individuals with obesity and a positive risk association. The wide range of objective and subjective measures, methods and cut-offs resulted in great variations of physical inactivity and sedentary behavior estimates. TRIAL REGISTRATION: PROSPERO (CRD42016037747).