Poor adherence to lifestyle intervention remains a key factor hindering treatment effectiveness and health outcomes for adults with obesity. The aim of this systematic review and meta-analysis is to determine if behavioural treatment strategies (e.g. goal setting, motivational interviewing, relapse prevention, cognitive restructuring etc.) improve adherence to lifestyle intervention programmes in adults with obesity. Randomized controlled trials that investigated the use of behavioural treatment strategies in obesity management were identified by systematically reviewing the literature within Medline, PsycINFO, CINAHL, SPORTDiscus and Web of Science from their inception to August 2016. This meta-analysis shows that behavioural treatment interventions have a significant positive effect on session attendance (percentage) and physical activity (total min/week) in adults with obesity (M = 17.63 (95% confidence interval (CI) = 10.77, 24.50), z =5.0337, P < 0.0001 and M = 105.98 (95% CI = 58.64, 153.32), z =4.3878, P < 0.0001, respectively). This meta-analysis of randomized controlled trials provides evidence that behavioural treatment strategies improve adherence to lifestyle intervention programmes in adults with obesity. These strategies should be routinely incorporated into lifestyle intervention, obesity management and weight loss programmes with the aim of improving engagement and adherence. If adherence were improved, treatment effectiveness, health outcomes and the ultimate burden of chronic disease could also be improved.