Objectives: To (1) determine the weight-reducing effect of the Koa Family Program (KFP), a community-based, telewellness obesity intervention and (2) examine the impact of the KFP on improving weight-related health indicators. Design: Randomised controlled trial. Setting: Community-based in Sacramento, California, USA. Methods: Seventy women with overweight or obesity (25 [less than or equal to] BMI < 40), aged 21-45 years and with low income ([less than or equal to] 185% of the US Federal Poverty Level) were randomly assigned to an intervention (n = 34) or control (n = 36) group. Data were collected by phone-administered questionnaire at weeks 0, 18 and 25. The intervention consisted of three components: (1) weekly, health coach-led, health education meetings on Zoom; (2) social media support through texting and private Facebook groups; and (3) a tree planting and stewardship campaign. The treatment effect on outcome measures (95% confidence intervals) was analysed with adjustment for variables including age, race/ethnicity, education and intake of fruit and vegetables. Results: The overall treatment effect of the KFP was weight loss at both Week 18 (-7.69 pounds [p < 0.000; 95% confidence interval (CI) = -11.97 to -3.41]) and Week 25 (-7.72 pounds [p = 0.002; 95% CI = -13.02 to -2.42]) of the study. KFP-associated improvements in diet, physical activity, stages of change and self-efficacy were also observed. Conclusions: The KFP resulted in weight loss significant at individual and population levels.