Scaled interventions are required to address levels of overweight and obesity and reduce health inequalities. Little data is available on the effectiveness of community weight management programmes for participants self-selecting to attend across different socio-economic backgrounds. This analysis investigates 3, 6, and 12-month outcomes of adults joining a real-life community weight management programme. Weight, attendance and Indices of Multiple Deprivation (IMD) data from all fee-paying adults joining Slimming World in 2016 were collated. Data were analysed using descriptive and inferential statistics to determine predictors of weight loss. Mean BMI of 1 094 676 adults (7.6% male) was 33.0 ± 6.4 kg/m2. Mean % weight change at 3, 6, and 12 months was -5.0% ± 3.6%, -5.9% ± 5.2%, and -6.0% ± 5.8%. Those attending 75% sessions achieved greater weight loss with mean weight losses at 3, 6, and 12-months of 7.7% ± 3.3%, 11.3% ± 5.2%, and 14.1% ± 7.5%, respectively. Effect sizes from comparison of weight change between deprivation deciles were negligible, with similar outcomes in the most and least deprived deciles at 12-months (-5.7% ± 5.9% vs. -6.2% ± 5.9%). This service evaluation of more than 1 million adults attending a community weight management programme found they were able to achieve and/or maintain an average 6% weight loss at 12 months, with high attenders achieving >14% loss. Men and those with higher levels of deprivation were accessing the support and achieving significant weight losses. Slimming World as a real-life, scalable weight management programme is well placed to help adults manage their weight and address health inequalities.